Special issue for Klaus Gawrisch

What defines a highly respected scientist? There are many scientists who are outstanding in different aspects of our daily work, great mentors, great friends, great synthesizers, great reasoners, great experimentalists, great innovators, etc., but there is not a single formula. Nevertheless, when there is a groundswell of gratitude, concern, and an overwhelming sense of imminent loss among so very many biophysicists, we are certainly justified in paying a tribute to a scientist who preferred to consider himself just one expert among many. This special issue of Biophysical Journal arises out of exactly that scenario, and the huge energy of many of us was unambiguous in our determination to single out Klaus Gawrisch to honor for his many, many great attributes, including all of those above. Indeed, many of us have been depending on Klaus for his unsurpassed expertise on the nuclear magnetic resonance (NMR) of lipids and mixtures of lipids in membranes and the subtle but essential ways that lipid handling, the choice of solvents and detergents, and osmotic stress impact lipid and membrane protein hydration and configurations. "When stuck, call Klaus” has been excellent advice for many years. He has generously responded with long discussions replete with wisdom, data, and references, outlining with great mastery what should and should not be done. His authority is based on a lifetime of accumulating experimental data with his own hands on many different aspects of the chemical interactions of lipids and membrane proteins, as well as many interactions with collaborators with whom he widened his expertise.

Son of a carpenter, Klaus was born in the last hours of 1950 in Freyburg, East Germany, where he trained as a mason in high school. This culminated in very high scores on the Abitur exams, resulting in Klaus being invited to study physics at Moscow State University (MSU), where he worked with N.N. Sergeyev on shift reagents in ¹³C NMR in the laboratory of biophysics led by Prof. Lev A. Blumenfeld. More importantly, Klaus met his wife Ludmila Archipowa, also an undergraduate at MSU in physics and the chief cook in the summer construction work program in the village of Chemodanovo (about 300 miles northeast of Moscow), where he was assigned. They married in 1972 and have two children and two grandchildren.

After he earned his MS degree at MSU, Klaus and Ludmila moved to Leipzig, where Klaus worked in the physics department of Karl Marx University (the name for the University of Leipzig between 1951 and 1991). There, in the Laboratory of Molecular Physics, led by Prof. Dr. G. Klose, Klaus first studied with advisor Prof. Dr. K. Arnold on “³¹P and ²H NMR investigations of molecular motions in phospholipid water dispersions,” earning the Dr. rer. nat. (PhD) in 1979. In a second doctoral degree, Klaus studied the “molecular mechanisms of the polyethylene glycol induced cell fusion” with both Drs. Arnold and Klose, resulting in his doctor of science (Dr. sc. nat.) degree in 1986. By this point, Klaus had risen from assistant at the Laboratory of Molecular Physics to associate professor of biophysics at the Laboratory of Physics of Condensed Matter in the physics department, where he had become facultas docendi (University Lecturer) in 1985.

Because of his outstanding work on each of these two subjects, Klaus was awarded the Leibniz Prize of the University of Leipzig in 1981 for education, training, and research and the best paper award at the 1985 International Scientific Conference on Membrane Organization for his work on the NMR of hydration forces. Dr. V. Adrian Parsegian attended this meeting, leading to Klaus’s invitation to join us in his laboratory at the NIH as a visiting fellow, the first one from the former Soviet Union in our experience. Despite a number of hardships, including waiting 2 years for permission to leave the GDR (granted only with retention in East Germany of Ludmila and their two children, Roland and Michael) and returning to a post-doc salary after achieving associate professor with tenure, Klaus readily accepted Parsegian’s invitation because “he wanted to be where the science was being made.” Luckily, the collapse of the Soviet Union allowed an opening of the borders about a year later, allowing Klaus to stay and for his family to ultimately join him.

Despite his post-doc salary and the determination of Ludmila and Klaus to allow their children to complete their German education through the Abitur (private school), and Ludmila’s lack of a work visa, they managed to survive the high-cost locale of Bethesda, MD, USA, mainly through Ludmila’s expertise in cooking and sewing. This all changed when Klaus and Ludmila got their green cards, and Ludmila aced the Microsoft networking exams, allowing her to have a long-term job with the National Abortion Federation running their IT department, which she grew from two individuals on a phone line to a staff of 40, servicing the US, Canada, and Mexico with free information. Ludmila was simply shocked that here, in America, some men were making decisions about a woman’s body and that we were so far behind other nations, so she took the job despite the risks to herself and family. Indeed, she knew some of the murdered abortion providers, some killed in their churches.

Klaus was soon able to start his own group by moving to another institute, first as a tenure track and then a senior investigator when he got tenure on January 15, 1998. His group, the Laboratory of Membrane Biochemistry and Biophysics, is still extant despite his retirement in 2020.

The following paragraphs highlight some of Klaus’s work.

From early on in his career, Klaus was contributing to the phase behavior of lipids in bilayers (1,2,3,4,5,6,7,8,9,10,11,12,13,14). This groundbreaking work was interspersed with studies on the interactions of lipids with solvents, ions in membrane bathing solutions, and the interactions of an amphipathic peptide from the HIV spike protein C-terminal tail (4,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40), and many papers on lipid syntheses and spectra of newly purified lipids (see supporting citations). His first two papers with Adrian Parsegian and Peter Rand and their colleagues were very influential. First, the study of the reentrant phase of phosphatidylethanolamine, a biphasic phase change between lamellar and inverse hexagonal phase with varying osmotic stress, led to a better understanding of lipid energetics under stress (12). Second, the finding that the repulsive hydration force between bilayers originated from disruptions in the H-bonding network between waters bound to the phosphate and to embedded waters in the headgroup region had broad implications to the forces between other substances, such as DNA, carbohydrates, and proteins (33). Klaus’s work with Sarah Keller and Sarah Veatch (41,42,43) on the equilibrium of liquid-ordered (Lo) and liquid-disordered phases in bilayers had a profound influence on the field and set the stage for understanding lipid rafts in cell membranes. Quite remarkably, the first paper in this series went from a question they posed to Klaus at a Biophysical Society (BPS) subgroup meeting to a nearly fully formed story after only 2 weeks of research in Klaus’s lab, collecting spectra by day and trying to keep up with the analysis by night. Tie-line measurements extracted from NMR spectra brought Klaus’s characteristic rigor to semi-quantitative observations previously made using fluorescence microscopy while drawing connections to past studies on membranes of cholesterol and phospholipids. Subsequent measurements used NMR line broadening to identify fluctuations in membranes poised near miscibility critical points, an alternative mechanism for membrane organization on submicron length scales (43). Klaus then helped guide the simulation paper showing that the structure of the Lo phase consisted of patches of highly ordered (gel-like) saturated lipids with less ordered boundary regions of unsaturated lipid and cholesterol (44). A few years later, Klaus took the electron paramagnetic resonance measurements showing that oxygen was nearly as likely to be in the midplanes of an Lo phase as the liquid disordered one, providing critical experimental support for simulations detailing the pathway of oxygen permeation through the Lo phase (45).

Klaus often responded to scientific questions by “this should be done with Kernresonanz” (using the German word for NMR spectroscopy). And of course, he really knew a way to utilize NMR to solve it. In the mid 90s, Klaus was one of the first to recognize how nuclear Overhauser enhancement spectroscopy (NOESY) could be adapted to lipid membranes using ¹H magic angle spinning (MAS) (46). Klaus’s work with Daniel Huster converted ¹H MAS NOESY into a tool for quantitative membrane structural studies and demonstrated that membranes are characterized by a tremendous degree of motional disorder (47,48,49,50). Together with Bill Wimley and Steve White, Klaus used ¹H MAS NOESY to show the preference of tryptophan for the membrane interface, which is to date his most highly cited paper (51). Since then, the use of ¹H MAS NOESY NMR has evolved into a major tool in the arsenal of NMR spectroscopists for the study of membrane binding, organization, localization, and orientation of membrane embedded molecules (52,53,54,55). Klaus’s work on ¹H MAS NOESY NMR was also instrumental to what has been his lifetime interest: understanding how membranes rich in polyunsaturated lipids like DHA differ from less unsaturated ones. After early ²H NMR studies with Frances Separovic and Bernd Koenig on the influence of chain unsaturations on lipid bilayers (56,57,58,59), Klaus told us why bilayers with high DHA content have low order (60), how the loss of one double bond affects bilayer properties (61), and how polyunsaturation may affect protein function (62,63) and membrane fusion events (64). Klaus’s work over the past 30 years has been foundational to our understanding of the biophysical properties of polyunsaturated lipid bilayers (59,61,65,66,67,68,69,70,71,72,73,74,75,76,77). This work also led him to become an advocate of eating fish (78). Anecdotally, he always urged his friends to eat fresh salmon immediately after a quick cooking, before many of the double bonds were oxidized!

In the late 90s, Klaus developed the use of pulsed magnetic field gradient MAS ¹H NMR to study the lateral diffusion of water, lipids, and drugs in the lipid matrix (79,80,81,82). Klaus’s work on the detection of lipid domains in model and viral membranes with Joshua Zimmerberg using pulsed magnetic field gradient MAS ¹H NMR had a profound influence on the field (83,84). His ¹³C T₁ relaxation measurements of liposomes combined with simulations by Jeff Klauda and Rich Pastor helped to clarify the issue of collective and noncollective motions in bilayers (85). Some of Klaus’s more recent contributions with Ella Mihailescu are a fantastic nod to his early interest in the role of hydration (86,87,88,89).

In the early 2000s, Klaus became interested in G protein-coupled membrane receptors (GPCRs). Klaus’s decade-long work with Olivier Soubias revived lipids as important modulator of GPCRs function (90,91,92). Klaus told us about the many ways by which the thermodynamic and kinetic equilibrium between functional states of the GPCR rhodopsin is linked to properties of the lipid bilayer via lipid-protein interactions (63,74,93,94,95,96,97,98,99,100,101). In parallel, he became interested by lipid-like endocannabinoid ligands and their interaction with cannabinoid receptors. Klaus’s work with Alexey Yeliseev on the expression (102,103,104), purification (105,106,107), and stabilization (108,109) of the cannabinoid receptor type 2 in a functional form and in quantities large enough for NMR studies paved the way to study its global fold in membranes (110,111) and its sensitivity to lipid composition (112,113). In parallel, Klaus elucidated how lipid-like GPCR ligands access their targets from the membrane (55,114), setting the stage for the next generation of discoveries (115,116).

Klaus’s training in physics made him the ideal experimental collaborator in projects involving molecular dynamics simulations. He understands the limitations of timescales, computers, and the underlying theory of the simulations and never asks for too much or too little. Collaborations often began with him saying “I can measure that for you,” and he would teach us what we needed to know about his experiments. Klaus also has a knack for spotting connections between his measurements and surprising simulation results. For example, over beers at a BPS meeting, he explained the increased internal hydration of rhodopsin and its sensitivity to the protein’s state observed in simulations via some NMR experiments he had carried out but hadn’t published (117). Klaus helped start the independent research careers of Scott Feller with studies of polyunsaturated lipids (60,61,62), Alan Grossfield with GPCRs (110,114,117), Ed Lyman with the structure of Lo phases (44), and An Ghysels with oxygen permeation in this phase (45). He contributed to lipid force-field development by his NMR measurements of anionic lipids (118).

Klaus has been a long-time member and contributor to the BPS. He published 22 papers in Biophysical Journal. He served for two terms on the board as an editor with a strong commitment to maintain high standards and, at the same time, give constructive advice to authors to help them publish. He chaired the Membrane Structure and Assembly Subgroup and served on the awards committee. In 2007, he received the BPS Avanti Award in Lipids.

This issue contains 17 papers by friends of Klaus Gawrisch covering many areas, all where Klaus has made contributions.

Editor: Vasanthi Jayaraman.

Supporting citations

Klaus Gawrisch's papers not already cited in this Introduction: 119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174.