�9 1990 by The Humana Press Inc. All rights of any nature whatsoever reserved. 0163-4992/90/1612--0099502.00

BOOK REVIEW

Membrane Proteins: Structure, Function, Assembly

Nobel Symposium #66

J. RYDSTROM, ED. The Royal Swedish Academy of Sciences, Chemica Scripta,

vol. 2 7B, 198 7, Cambridge University Press, ISBN 0-521-35586-9(hb) ISBN 0004-2056(pb)

This volume contains the proceedings of the September, 1986 (not 1987, as claimed on the title page) Nobel symposium held at Alfred Nobel's house in Karlskroga. It is one of a series that seem, in part, to represent the Nobel committee's attempts to inform itself of developments in key areas of an increasingly cooperative scientific endeavor prior to the award of the very individualized Nobel prizes. In this case, the symposium was followed by the award of the Chemistry prize to'the Deisenhofer, Michel and Huber group in 1988. Each article comprises a brief review O f part of the field, usually from the standpoint of the author's own research inter- ests, together with some exemplary new, or at least recent, results. What does the book tell us about the contemporary quality of the membrane protein business?

First and foremost it seems to emphasize in some respects the increas- ing "homogenization" of biology. The classical emphasis on the genera- tion and solution of defined problems of all kinds--a kind of traditional "miniphysics"--has given way to a new kind of natural history--the complex natural history of the genome. The major premium is now on new methodologies rather than on ideas--ways of running and analyzing gels of proteins and nucleic acids and their degradation products that per- mit a finer and finer analysis of the molecular events that lead to the acti- vation of the gene and the formation of the protein.

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What makes this particular compilation a discussion of membrane proteins rather than any other kind? First, the search for crystals permit- ting X-ray structural analysis--long a standard procedure with nearly all soluble proteins but, as yet, except for the prize-winning example from Michel's laboratory (described on pp. 173-180), only a hope for the mem- brane group. Second, the search for other ways of determining structure-- the identification of transmembrane helices by appropriate algorithms and to determine chemically, immunologically, and biochemically the ori- entation of reactive groups on the two ends of protein molecules "plugged through" phospholipid bilayers. Third, the attempt to define function in terms of the transmembranous activity of such "plugged-through pro- teins" and their responses to the two milieux--inside and outside the organelles in which they function.

Yet that brave new world that the award of the 1978 chemistry prize to Peter Mitchell seemed to foreshadow--the world of vectorial chemistry and topobiochemistry--seems already to be a thing of the past. Perhaps it was not as fruitful--as heuristically valuable--as we had hoped. Certainly today Michel, not Mitchell, rules OK. Who is represented here of the sev- eral persuasions of membrane proteinology, which trends do they exem- plify, and how do they compare?

The book is divided into six sections, covering (i) receptors and chan- nels, (ii) electron transport, (iii) ATPases, (iv) reaction centers and light- reactive proteins, (v) lipid-protein interactions, and (vi) biosynthesis and assembly. It is the first that clearly makes the most serious attempt to unite the old and the new worlds. Numa presents complex comparative lists of amino acid sequences and gene structures and also tries to match those findings with electrical events observed with the products (proteins and mRNAs) under patch clamp conditions. Wikberg's contribution is, however, almost entirely phrased in the style of the new cell biology. Rosenbusch, on the other hand, attempts to create a physicochemical model of sodium conductance using current structural information but in the model-building style of yore. Klingenberg simply shows that there are homologies between the three mitochondrial carriers of phosphate, ATP/ADP, and hydroxyl ions (uncoupling protein of brown fat). Unwin presents a structural but not a functional mode of cell communication channels, based on electron image analysis of two-dimensional "crystals" of acetyl choline receptors.

In the electron transfer section, Wikstrom and Malmstrom struggle bravely with the complexities of functional behavior shown by cytochrome c oxidase, and come up with interesting "models" of the classical kind (i.e., based on analysis of kinetics and partial reactions rather than struc- tural studies). Yet they have Roderick Capaldi breathing down their necks with his ongoing efforts at structural and molecular definition of this most central but so far most intractable bioenergetic complex. Structural infor- mation may arrive sooner for the other respiratory complexes, as sug- gested by Weiss' work with coenzyme Q reductase and oxidase systems.

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Functionally, the clearest contribution is made by the editor himself, who sets a good example to his coauthors with a description of the transhydro- genase--including sufficient structure to orient, and sufficient function to interest without losing the reader. This single polypeptide enzyme ought surely to be a candidate for a more decisive structural attack.

Such a study is represented in this book by the kind of work being carried out by Khorana and his ten listed coworkers on bacteriorhodopsin --one of the most determined and single minded efforts going on in this area--almost entirely employing the methods of the new molecular world. Yet one wonders--is this study of one of the more unusual transmembrane proteins synthesized by the evolutionarily strange halophilic bacteria really worth the enormous effort being put into it? Are we seeing the result of crystallographic frustration? My own research team would doubtless be most usefully absorbed just into the coffee-making section of Khorana's midnight oil burners. But if we choose not to do this (the Canadian grant agency NSERC might not encourage such altruism, anyway), and instead work by ourselves, do we really achieve anything? At least they are secur- ing sequences, data concerning important and unimportant residues-- whereas we are still trying to create global models of much more complex systems, such as the mammalian oxidase, whose structure we understand much less well. It is hard to decide.

The most complex enzyme family being analyzed by the molecular juggernaut is clearly the ATPase. Even larger than the oxidase, its genetics are somewhat better understood because it is found in classical eukaryotes such as E. coli. Walker and his group try to draw the big comparisons, Futai et al. to do the functional "fine structure analysis" using mutants. This enzyme has the advantage that it clearly divides into peripheral F1 and membrane-penetrating F0 components, which can be studied inde- pendently. Would that the oxidase had been designed along similar lines. Why wasn't it? At any rate, one wonders why the F1 enzyme has not been crystallized. We think we know where it is relative to the F0 component, so that should provide us with many clues. We await developments. Cer- tainly, it is becoming clearer that substantial separation occurs between the sites of biochemical (ATP-hydrolyzing) activity and of ion transport, not only in the H§ but also, and perhaps specially in the Ca 2+- ATPases, described by de Meis and Carafoli (and the subject of a compara- tive analysis by Norby).

Khorana's focus on bacteriorhodopsin is extended by the late Yuri Ovchinnikov in a comparative study of the light receptor proteins as com- pared with ion pumps. His essentially molecular approach is comple- mented by Stryer's attempt at a functional and kinetic analysis of the visual transduction cascade that remains contemporary while ignoring molecu- lar minutiae and concludes with the famous quotation from Darwin's Origin on the "eye" . The photosynthetikers have adopted one of two tacks after the Michel-Deisenhofer success. One, taken by Andersson and others not represented here, is to try to analyze the plant systems in terms

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of the known bacterial structures, fitting in the extra or different pieces by analogy, by mutation, or immunochemical studies. The other approach, exemplified here by Jan Anderson and in a short but elegant paper by Per Albertsson, is to begin looking at the lateral arrangement of the several complexes within the thylakoid membranes, a subject of considerable in- terest in view of the strict separation of the two photosystems between appressed and nonappressed regions despite their needed functional connection in electron transfer. This is the kind of problem that neither crystal analysis nor genetic sequencing are likely to contribute to in the near future.

The lipid-protein interaction section is a little disappointing to this reviewer. Perhaps we still need a satisfactory theory of protein-phospho- lipid interactions in membranes before such studies can bring a sense of constructive analysis similar to that achieved with the proteins alone (or arranged in the symbolic membranes favored by the enzymologists). The biosynthesis section (two papers only, one from Sweden, one from the USA) seems to have been included as something of an afterthought. Blobel was apparently present but did not submit a paper. (There are several senior workers listed as participants who may be in this category. Can submission not be required as a condition of participation? The committee should try to keep a complete record of its proceedings.) None of several other currently acknowledged field leaders (Schatz, Neupert, et al.) are here. They may, we can hope, be invited to another symposium a few years from now, when membrane protein synthesis and import mecha- nisms have reached a point that merits them for prize consideration.

Was the symposium as a whole representative of the field? Some biases can be discerned. Thus, Scandinavia seems a little overrepresented with 9/29 papers. The USA has 8/29, and the remainder come from Japan (2), Switzerland (2), the Federal Republic (3), with the UK, the USSR, France, Australia, and Brazil (sole third world representative) at one each. The reviewer could detect only one woman membranologist to 28 men. As pointed out at the beginning of this review, it is a very "molecular" com- pilation, and where not molecular, biochemical in its problem-solving ap- proach. There is no real attempt at biophysical analysis, with the possible exception of a small amount of material in the earliest section on recep- tors. In this way, it contrasts with a book such as Alan Finkelstein's Water Movement through Lipid Bilayers, Pores, and Plasma Membranes: Theory and Reality (1987), vol. 4 of the Distinguished Lecture series of the Society of General Physiologists (Wiley-Interscience, ISBN 0-471-84787-9), which happens to be on the reviewer's desk at the same time. Finkelstein is talk- ing about the same kinds of thing, commencing with an analysis of osmosis (from Pfeffer (1887) and Van't Hoff (1887) onward) and going on to lipid permeabilities, channel-formers, pores in plasma, and red cell membranes, and concluding with epithelial transport. It makes no concessions to the molecular world at all (well, photographs of molecular models of gramici-

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din and amphotericin are shown). It is entirely rigorous yet consistently readable, with a sense of history as well as of contemporary problem areas. It is the sort of book every biophysicist or cell physiologist should have on his/her shelves. It is the best scientific book I have seen for a while (per- haps along with the more popular "Q .E .D . " by the late Richard Feynman).

Can I say the same about the Nobel Symposium? Of course, it is not the same kind of book, and it doesn ' t try to do the same kind of thing. There are good things in it, including but not limited to the articles by Stryer and by Rydstrom. If you are a membrane proteinologist, you will need to be aware of nearly all the work going on that is described here. The easiest way to keep aware is to have a book like this of your own. But you may not prize it as you would a more personal study. And you will need to use it now. A few years hence it will be superseded.

Peter Nicholls Brock University

St. Catharines Ontario, Canada

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