Downloaded by 80.82.78.170 on January 9, 2017 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0602.pr001
Preface i H E S U R F A C E ACTIVITY O F PROTEINS is a fundamental property of these complex macromolecules that derives from their large size, amphipathic 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 biological properties of the interfaces. Proteins at interfaces are impor tant in many applied areas, including separation and purification, the biocompatibility of biomaterials, mammalian and bacterial cell adhesion, blood coagulation at solid and membrane surfaces, solid-phase immunoas says, biosensor development, the opsonization of particulates used as therapeutic agents, food processing, and biotechnology in general. Despite a fairly long history of study of proteins at interfaces, many of the fundamental mechanisms remain only partly understood, and research on proteins at interfaces remains very active. Reflecting the diversity of situations affected by proteins at interfaces, investigations in this area are also very diverse with respect to types of interfaces, proteins studied, methodology employed, and practical prob lems to which the work is directed. Consequently, research on proteins at interfaces is presented at diverse scientific meetings with typically only a few papers at each meeting. Similarly, the research is published in a wide variety of journals and other publications, resulting in very few comprehensive sources of information on this topic. By bringing workers from the many disparate application areas together into one symposium, 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 A C S 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 Horbett and Brash; Proteins at Interfaces II ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
Downloaded by 80.82.78.170 on January 9, 2017 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0602.pr001
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 motivated many of the researchers who study proteins at interfaces and whose work is described in this volume. However, its message can be transposed and applied to any complex biofluid. Vroman's introduction indicates, in a way that only a scientist-poet of long experience could, the complex nature of these interactions and warns us, lest we become prematurely smug, that we still have a long way to go in achieving any thing resembling a full understanding. T H O M A S A. H O R B E T T
Department of Chemical Engineering University of Washington Seattle, W A 98195-1750 JOHN
L.
BRASH
Department of Chemical Engineering McMaster University Hamilton, Ontario L8S 4L7 Canada June 28, 1995
xii Horbett and Brash; Proteins at Interfaces II ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
Downloaded by 80.82.78.170 on January 9, 2017 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0602.pr001
Prologue i H E MOST COMPLICATED L A N G U A G E 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 then can we ever hope to read the significance of such a briefly present and changing text and context? Perhaps we have been very slow to face this problem, misled since we invented glass test tubes, especially once we learned to put blood in them that had been anticoagulated and could be swung around to separate its deceptively simple-looking plasma. Slowly it dawned on us that the resulting interactions were far from simple, and we now know that on many surfaces, outrageously complex protein mixtures such as blood plasma write their own opinions by means of adsorbing and interacting protein molecules. Of course our blood's authorship did not evolve to entertain us; it merely tries to protect us. I am sure that any spilled blood is not aware of having left its host forever, nor of the relative immensity of foreign surface it faces. A l l interactions with this surface are aimed at protecting the host against what this poured blood perceives as an invasion of its host's body by strange and unfathomed matter. Thus it is the blood itself that is doing the reading. It reads the sur face properties with the help of its own proteins and passes the informa 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 ( H M K ) xiii Horbett and Brash; Proteins at Interfaces II ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
Downloaded by 80.82.78.170 on January 9, 2017 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0602.pr001
could not remove fibrinogen before the platelets arrived. Immediately beyond this spot, where H M K 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 cell surfaces do not exist until they are dead. Even single purified pro teins must be suspected of not behaving as they would normally in the environment where they evolved their specific and often unknown func tions. We can create surfaces now that vaguely resemble cell surfaces, e.g., by coating materials with phospholipid bilayers. The mobility of molecules in such a coating lets it respond to very local events, such as the approach of a protein molecule. If it is true that a protein molecule simply cannot attach itself on such a "soft" surface and will not be forced to spread, the complexity of such an interaction has been taken away from this protein molecule and transferred to the substrate. When we attempt to write on oatmeal, the invisible words may still change the oat meal. Such interactions between surface and proteins, and between adsorbed and hence modified proteins and formed elements, are echoed in this volume by the interactions among those scientists who study them. LEO VROMAN
Department of Chemical Engineering, Materials Science, and Mining Columbia University 500 West 120th Street New York, N Y 10027 June 29, 1995
xiv Horbett and Brash; Proteins at Interfaces II ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
