Table Of ContentACS SYMPOSIUM SERIES 602
Proteins at Interfaces II
Fundamentals and Applications
Thomas A. Horbett,
1 EDITOR
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w0 University of Washington
2.f
0
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995- John L. Brash, EDITOR
1
bk- McMaster University
1/
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0
1
0.
1
s.org 5 | doi:
c9
s.a19
ub5, Developed from a symposium sponsored
p://pMay by the Division of Colloid and Surface Science
12 | httDate: at the 207th National Meeting
August 16, 20 Publication of the SAaMmna eDrrciicheag 1no3 ,C -C1h7aelm,i f1oic9ra9nl4i aS ,o ciety,
American Chemical Society, Washington, DC 1995
In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
Library of Congress Cataloging-in-Publication Data
Proteins at interfaces II: fundamentals and applications / Thomas A.
Horbett, John L. Brash, editors.
p. cm.—(ACS symposium series, ISSN 0097-6156; 602)
"Developed from a symposium sponsored by the Division of Colloid
and Surface Chemistry at the 207th National Meeting of the American
Chemical Society, San Diego, CA, March 13-17, 1994."
Includes bibliographical references and index.
1
0 ISBN 0-8412-3304-7
0
w
2.f 1. Proteins—Congresses. 2. Surface chemistry—Congresses.
60 3. Biological interfaces—Congresses.
0
5-
9 I. Horbett, Thomas A, 1943- . II. Brash, John L., 1937-
9
1 III. American Chemical Society. Division of Colloid and Surface
k- Chemistry. IV. American Chemical Society. Meeting (207th: 1994:
b
1/ San Diego, Calif.) V. Series.
2
0
1
0. QP551.P697782 1995
s.org 5 | doi: 1 574.19'245—dc20 95-368C6I3P
c9
s.a19
p://pubMay 5, This book is printed on acid-free, recycled paper.
12 | httDate: Copyright © 1995
August 16, 20 Publication AAcchhlmaal ppeRrtteeiicgrrah inmtns C a tRhyhi eesbms eevri ocvmaleuldam Sd. oeecT iifnehotdeyri c aappteeprses aotrnhaaenl c ceoo proy firn igtthehretn oacwol dnueesr e'as toc roth nfesoe rnb ott thtthoea mtp eroresfpo rtnohagelr afopirrhs iticn pcteoargpnieae slo fou fse eat hcohef
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PRINTED IN THE UNITED STATES OF AMERICA
In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
1995 Advisory Board
ACS Symposium Series
Robert J. Alaimo Cynthia A. Maryanoff
Procter & Gamble Pharmaceuticals R. W. Johnson Pharmaceutical
Research Institute
Mark Arnold
University of Iowa Roger A. Minear
University of Illinois
David Baker at Urbana-Champaign
1 University of Tennessee
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0 Omkaram Nalamasu
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2.f Arindam Bose AT&T Bell Laboratories
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6 Pfizer Central Research
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5- Vincent Pecoraro
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19 Robert F. Brady, Jr. University of Michigan
bk- Naval Research Laboratory
21/ George W. Roberts
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1 Mary E. Castellion North Carolina State University
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1 ChemEdit Company
s.org 5 | doi: Margaret A. Cavanaugh JUonhivne rRsit.y Sohf aIpllilneoyi s
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s.a19 National Science Foundation at Urbana-Champaign
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p://pMay Arthur B. Ellis Douglas A. Smith
12 | httDate: University of Wisconsin at Madison Concurrent Technologies Corporation
August 16, 20 Publication GUMUnnuaiivnvdeederralsseii ttiIyyn. eooG ff MeKPoea.nr nJgnsoas yusl vllainei a LDMP.au irPcSkohoen-amDte aal vsDiusn . PTdhaaarrymalomarc eutical Research
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In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
Foreword
IHE ACS SYMPOSIUM SERIES was first published in 1974 to
provide a mechanism for publishing symposia quickly in book
form. The purpose of this series is to publish comprehensive
books developed from symposia, which are usually "snapshots
in time" of the current research being done on a topic, plus
some review material on the topic. For this reason, it is neces
sary that the papers be published as quickly as possible.
1
0
w0 Before a symposium-based book is put under contract, the
2.f proposed table of contents is reviewed for appropriateness to
0
06 the topic and for comprehensiveness of the collection. Some
5-
9 papers are excluded at this point, and others are added to
9
1
k- round out the scope of the volume. In addition, a draft of each
b
1/ paper is peer-reviewed prior to final acceptance or rejection.
2
10 This anonymous review process is supervised by the organiz
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1 er^) of the symposium, who become the editor(s) of the book.
s.org 5 | doi: Tmheen daauttiohnosr s otfh ebno rthev itshee threeivri epwaepresr sa nacdc otrhdei negd tioto rtsh,e prreecpoamre
c9
s.a19 camera-ready copy, and submit the final papers to the editors,
ub5,
12 | http://pDate: May wvihewo cAphsa epcaek r rsthu aalert, e a olinln lncyle ucodersesidga irinyna lrt herveei ssevioaonrlucshm h eapsva.e p ebVreeser nba anmtdiam do err.ie gpinroadl urec
August 16, 20 Publication tions of previously published papers are not accepted.
In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
Preface
iHE SURFACE ACTIVITY OF PROTEINS is a fundamental property of
these complex macromolecules that derives from their large size, amphi-
pathic nature, and the many types of chemical interactions that can occur
between proteins and surfaces. Thus interfaces of almost any type that
come into contact with protein solutions tend to become quickly occupied
by proteins, leading to profound alterations in the physicochemical and
1
00 biological properties of the interfaces. Proteins at interfaces are impor
2.pr tant in many applied areas, including separation and purification, the
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6 biocompatibility of biomaterials, mammalian and bacterial cell adhesion,
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95- blood coagulation at solid and membrane surfaces, solid-phase immunoas
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k-1 says, biosensor development, the opsonization of particulates used as
1/b therapeutic agents, food processing, and biotechnology in general.
2
0 Despite a fairly long history of study of proteins at interfaces, many of the
1
10. fundamental mechanisms remain only partly understood, and research on
cs.org 95 | doi: protReienfsle actti ningt etrhfea cdeisv erresmitayi nosf vsietruya taicotnivse a. ffected by proteins at interfaces,
a9
p://pubs.May 5, 1 iilennmtveesrs ftatiogc aewsti,ho nipcsrh o ittnhei ent hsw isos truakrd ieisea d da,i rrmeec etatelhdsoo. d vCoeloorngyys ed qievumeerpnslteol yyw,e ridte,hs earanerdscp hpe crotan c ttpoicr aotlyt eppienrsso boaft
2 | httDate: interfaces is presented at diverse scientific meetings with typically only a
01n few papers at each meeting. Similarly, the research is published in a wide
2o
16, cati variety of journals and other publications, resulting in very few
August Publi fcroommp rthehee mnsaivney sdoiusprcaersa toef aipnpfolircmataiotino na roena st htiosg teothpeicr. inBtyo bornineg isnygm wpoorsikuemrs,
we believed we could provide a means to foster advances in proteins at
interfaces via presentation of the many common concepts and approaches
embodied in the diverse systems and applications being studied.
To make participation in the symposium on which this book is based
as comprehensive as possible, we began more than a year in advance by
inviting many, if not most, of the investigators actively involved in studies
of proteins at interfaces to participate, and we subsequently included their
contributions in this book. This volume is similar in its intent to ACS
Symposium Series 343, Proteins at Interfaces, edited by us in 1987, but the
approach we have taken to the content is somewhat different. In the pre
vious volume, we invited overview chapters, whereas in this volume, the
chapters are similar to journal articles that reflect the current interests
and work of each group.
xi
In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
This book provides a broad collection of articles on the behavior of
proteins at interfaces, most of which derive from recently completed
investigations focusing on topics of current interest. The major themes
include molecular mechanisms, competitive adsorption, conformation of
proteins at interfaces, surface chemistry effects, protein effects on cell
interactions, and the behavior of proteins at fluid-fluid interfaces.
We believe this book can provide a sound introduction for those new
to the field but will have its greatest impact as a convenient way for
experienced investigators to broaden their understanding of the behavior
of proteins at interfaces.
The introduction by Leo Vroman, surely the expert's expert on pro
tein interfacial interactions in "outrageously complex protein mixtures",
relates specifically to blood-material interactions, phenomena that have
1
0 motivated many of the researchers who study proteins at interfaces and
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pr whose work is described in this volume. However, its message can be
2.
60 transposed and applied to any complex biofluid. Vroman's introduction
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5- indicates, in a way that only a scientist-poet of long experience could, the
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1 complex nature of these interactions and warns us, lest we become
k-
b prematurely smug, that we still have a long way to go in achieving any
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02 thing resembling a full understanding.
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0.
1
cs.org 95 | doi: TDHepOaMrtAmS eAn.t HofO CRhBeEmTTic al Engineering
ubs.a5, 19 USenaitvteler,s iWty Aof 9W81a9sh5i-n1g7t5o0n
p://pMay
012 | httn Date: JDOeHpNa rtLm. eBnRt AoSfH C hemical Engineering
2o
16, cati McMaster University
August Publi HCaanmaidltao n, Ontario L8S 4L7
June 28, 1995
xii
In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
Prologue
iHE MOST COMPLICATED LANGUAGE we can ever attempt to learn is
the one spelled by the proteins within us and rapidly written by them on
any blank surface they face. Each of the "words" is long enough to fill an
entire page if printed legibly, and as they are being "written" on the blank
surface, they may rapidly change their meaning or, in the presence of
more protein species, be displaced by a succession of these others. How
1
0 then can we ever hope to read the significance of such a briefly present
0
2.pr and changing text and context?
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6 Perhaps we have been very slow to face this problem, misled since we
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95- invented glass test tubes, especially once we learned to put blood in them
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k-1 that had been anticoagulated and could be swung around to separate its
b
1/ deceptively simple-looking plasma. Slowly it dawned on us that the
2
0 resulting interactions were far from simple, and we now know that on
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10. many surfaces, outrageously complex protein mixtures such as blood
cs.org 95 | doi: pplraostmeian wmroitleec uthleesir. own opinions by means of adsorbing and interacting
a9
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2 | httDate: surface it faces. All interactions with this surface are aimed at protecting
01n the host against what this poured blood perceives as an invasion of its
2o
16, cati host's body by strange and unfathomed matter.
August Publi faceT phruosp ietr tiise sth we itbhl otohde ihtseelplf othf aitt si so wdnoi npgr ottheein rse aandidn gp.a sIste sr etahdes inthfoe rsmuar
tion on to others: the intrinsic clotting system, the complement system,
and from there to the platelets and white cells that may arrive just in time
to read a few code elements exposed by some of the plasma's "written
words"—protein epitopes that these cells and platelets are tuned to by
their receptors.
So it is not surprising that we can find a wild paradise of elements left
on devices that blood has streamed over. Fixed and stained, it represents
a rather slow snapshot of a few physiologically significant and not entirely
simultaneous events that were driven by very local conditions. For exam
ple, we found that heparinized blood injected between a glass slide and a
convex lens resting belly-down on the slide may leave a small ring of pla
telets surrounded by a fine line of fibrin. What happened, we believe, is
that platelets adhered where high molecular weight kininogen (HMK)
xiii
In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
could not remove fibrinogen before the platelets arrived. Immediately
beyond this spot, where HMK did compete successfully for the surface,
the clotting system was activated next to the area where heparin had been
neutralized by platelet antiheparin activity so that fibrin could form.
A reasonable and yet naive question is what keeps our plasma from
writing its graffiti on the surfaces of all cells floating in it? And if we
create surfaces resembling those of cells, would proteins not be adsorbed
on them? Only the second question allows experimentation and can be
answered. There is no logical way of separating or cultivating normal
healthy cells in total absence of added or generated proteins in their
medium. Our ability to separate cells from their plasma may let us forget
that these cells were born in plasma and have been exposed to hundreds
of proteins at their interfaces before we put our hands on them. Clean
1
0 cell surfaces do not exist until they are dead. Even single purified pro
0
pr teins must be suspected of not behaving as they would normally in the
2.
60 environment where they evolved their specific and often unknown func
0
5- tions.
9
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k-1 We can create surfaces now that vaguely resemble cell surfaces, e.g.,
1/b by coating materials with phospholipid bilayers. The mobility of
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0 molecules in such a coating lets it respond to very local events, such as
1
10. the approach of a protein molecule. If it is true that a protein molecule
cs.org 95 | doi: stoim spplyr ecaadn, ntohte a tctoamchp lietsxeitlfy oonf ssuucchh a a"ns oifnt"te rsuacrftaiocne ahnads wbielel nn otta kbeen f oarwceady
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2 | httDate: Such interactions between surface and proteins, and between
01n adsorbed and hence modified proteins and formed elements, are echoed
2o
16, cati in this volume by the interactions among those scientists who study them.
August Publi LEO VROMAN
Department of Chemical Engineering,
Materials Science, and Mining
Columbia University
500 West 120th Street
New York, NY 10027
June 29, 1995
xiv
In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
Chapter 1
Proteins at Interfaces
An Overview
John L. Brash1 and Thomas A. Horbett2
1Department of Chemical Engineering, McMaster University, Hamilton,
Ontario L8S 4L7, Canada
2Department of Chemical Engineering, University of Washington,
Seattle, WA 98195-1750
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5-
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19 Proteins at interfaces are involved in a wide variety of phenomena, including
bk- mammalian cell growth in culture, reactions to implanted biomaterials, growth of soil
1/
2 bacteria, and formation of organized layers of proteins at the oil/water and air/water
0
1
0. interfaces. This broad range of phenomena has attracted the interest of a
1
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a9
ubs.5, 1 conduct investigations that are unique with respect both to the particular protein/surface
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significant fraction of the workers who are actively involved in studying the behavior of
proteins at interfaces. We have therefore chosen to organize our overview around six
major aspects of protein behavior at interfaces which emerged from the Symposium.
These aspects are: (1) theory, including molecular mechanisms; (2) competitive
adsorption; (3) conformation and orientation of proteins at interfaces; (4) surface
chemistry effects on adsorption; (5) the behavior of proteins at fluid interfaces; and (6)
effects of proteins on cell interactions with surfaces. For each topic, current
understanding is briefly summarized, and the contributions of the articles in this volume
are then discussed. Inevitably this type of subdivision is to some extent arbitrary and
artificial, so there is some overlap of material from one section to another. We trust,
however, that on balance our approach will facilitate the readers' (as well as the authors')
task of understanding the state of the art in this field.
0097-6156/95/0602-0001$12.75/0
© 1995 American Chemical Society
In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
2 PROTEINS AT INTERFACES II
Theory and molecular mechanisms of protein adsorption
It is fundamental to recognize at the outset of this discussion that proteins are large,
amphipathic molecules. As a result they are intrinsically surface active, and one of their
natural habitats may be said to be in the interface between phases. This idea gains in
plausibility if one considers that within cells proteins are often membrane associated.
Thus it may be argued that to understand the behavior of proteins at interfaces is to
understand an important aspect their normal behavior. A good perspective for adoption
by the novice approaching this field is that all proteins adsorb to all surfaces. It is rarely
a problem how to achieve the adsorption of a protein, but rather how to prevent it.
Consequently, protein adsorption is the central event in the biofouling of surfaces.
The interactions recognized as occurring in protein adsorption are mostly
noncovalent, ie H-bonding, electrostatic, and hydrophobic interactions. Examples of
covalent adsorption (as opposed to intentional covalent immobilization) are rare. These
1
0 are the same phenomena that occur in small molecule adsorption. Protein adsorption is
0
ch distinguished by the large size of the adsorbate and by the fact that while adsorbed the
2.
0 protein can undergo various transformations, both physical and chemical. Apart from
6
0
5- the theoretical aspects of these transformations, which are of themselves of considerable
9
9 interest, they often entrain changes in the biological activity of the protein, eg enzyme
1
bk- activity.
1/
2 Most of the effects mentioned have been recognized for many years and we will
0
0.1 not attempt to review the relevant literature in detail. Rather a few examples of recent
1
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ubs.5, 1 continue to fit adsorption data to the Langmuir equation despite its obvious
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been made from such data fits, although there is considerable scepticism about this
practice. Such estimates should strictly speaking not be considered as thermodynamic
equilibrium constants. They are at best apparent, and at worst pseudo binding constants.
However they can be regarded as giving a qualitative indication of binding affinity.
This more conservative approach to the interpretation of isotherm data is
illustrated by the work of Norde and Anusiem (/) on BSA and lysozyme adsorption to
silica and hematite. In this work the relative values of the initial isotherm slopes for a
series of protein-surface systems were interpreted in terms of the relative adsorption
affinities. An interesting result from these studies was that BSA that had been adsorbed
and then desorbed showed higher affinity than native BSA, suggesting that adsorption
caused a significant physical transition in the protein. No such effect was found for
lysozyme, a smaller protein also considered to be "harder" than BSA.
The paper by Norde and Haynes in this volume takes yet another look at
reversibility of protein adsorption. It shows that significant internally created entropy
In Proteins at Interfaces II; Horbett, T., et al.;
ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
