H. Ronald Kaback, MD
Position Title:Distinguished Professor, Physiology
Distinguished Professor, Microbiology, Immunology & Molecular Genetics
H. Ronald Kaback, MD is a Distinguished Professor in the Department of Physiology in the David Geffen School of Medicine at UCLA.
He received a B.S. in Biology at Haverford College in 1958 and an M.D. from the Albert Einstein College of Medicine in 1962.
As a medical student, he ‘discovered’ bacterial membrane vesicles and became intrigued with membrane transport while working in the
laboratory of Adele Kostellow in the Physiology Department at Einstein.
After receiving his M.D., he served as an intern in Pediatrics at the Bronx Municipal Hospital Center in 1963 and then spent a year
as a graduate student/postdoctoral fellow in the Physiology Department at Einstein.
In 1964, he became a Commissioned Officer in the United States Public Health Service at the National Institutes of Health in the
National Heart Institute (now the National Heart and Lung Institute) in the enzymology laboratory of Earl Stadtman, and in
1966, he became a Senior Research Investigator. In 1970, Kaback left NIH to become an Associate Member of the newly opened
Roche Institute of Molecular Biology in Nutley, New Jersey where he became Head of the Laboratory of Membrane Biochemistry in 1977 and
Chairman of the Department of Biochemistry in 1983.
In 1989, Kaback was recruited to UCLA in the Medical School as an Investigator of the Howard Hughes Medical Institute and
Professor in the Department of Physiology, as well as the Department of Microbiology,
Immunology & Molecular Genetics and a Member of the Molecular Biology Institute. Since 2004, he has been a Distinguished Professor.
Research Interests:
In 1960, the existence of cell membranes was questionable; let alone the presence of proteins that catalyze transport, when I discovered serendipitously that I could obtain empty membrane vesicles by osmotically lysing E. coli. Although the vesicles showed promise for studying transport, activity was low until it was discovered fortuitously that oxidation of D-lactate or later artificial electron donors yield activity comparable to intact cells. A plethora of studies demonstrated that the vesicles have the same orientation as the intact cell membrane, one of the most convincing being the demonstration that each vesicle catalyzes transport. These findings transformed membrane transport from phenomenology to biochemistry and laid the groundwork for vesicle systems from eukaryotic cell membranes, epithelia and intracellular organelles.
The lacY gene, the second structural gene in the lac operon, encodes lactose transport and provided the first evidence that proteins are involved in membrane transport. Thus, lactose permease (LacY) became a paradigm, and with the development of methodology to determine and quantitate membrane potentials (∆ψ) and pH gradients (∆pH), it became apparent that chemiosmosis is the thermodynamic basis for active transport of many solutes. LacY catalyzes an electrogenic reaction (lactose/H+ symport), and either component of ∆µ̃ H+ causes a 50-100 fold decrease in Km with little or no change in Vmax. Notably however, the KD for galactoside binding is the same from both sides of the membrane and unaffected by imposition of ∆µ̃H+
LacY is comprised of 417 amino-acid residues. In order to determine which residues play an obligatory role in the mechanism and to create a library of mutants with a single-Cys at each position of the molecule for structure/function studies, each residue was replaced with Cys in a Cys-less mutant. The great majority of >400 single-Cys mutants is expressed normally in the membrane and accumulates lactose against a significant concentration gradient, thereby demonstrating that Cys replacement at most positions does not induce severe perturbations in the structure of LacY or in the symport mechanism. Only 9 residues are irreplaceable for symport: Glu126 (helix IV), Arg144 (helix V), Trp151 (helix V), Glu269 (helix VIII), His322 (helix X), Tyr236 (helix VII) and Asn272 (helix VIII), which are directly involved in galactoside binding. Arg302 (helix IX) and Glu325 (helix X) are involved in H+ translocation.
In 2003, the first X-ray structure of a conformationally restricted mutant was solved at ~3.5 Å, and in 2006, a structure was solved at ~2.9 Å. In 2007, the structure of WT LacY was obtained at ~3.6 Å by ensuring that the protein was not depleted of phospholipid. The structures exhibit 12 transmembrane helices, many of which are distorted. The N- and C-terminal 6 helices form two distinct helical bundles with two-fold pseudo-symmetry surrounding a deep water-filled cavity. The cavity is open on the cytoplasmic side only, and the periplasmic side is tightly sealed (an inward-facing conformation). The structures suggest an alternating access mechanism in which the inward-facing cavity closes with reciprocal opening on the periplasmic side (an outward-facing conformation), thereby allowing alternating access of the sugar- and H+-binding site to either side of the membrane. Seven independent experimental approaches confirm the alternating access mechanism. Another X-ray crystal structure was obtained in 2014 with the double-Trp mutant G46W/G262W. Transport is abrogated in the mutant, but there is an increase in the rate of galactoside binding and an increase in affinity. Although the periplasmic side appears to be open in the absence of sugar, the 3.5 Å crystal structure contains a single bound galactoside, is narrowly open on the periplasmic side, and the cytoplasmic side is tightly sealed. The opening on the periplasmic side is sufficiently narrow that sugar cannot get in or out of the binding site.
Experimental findings garnered over 45 years have led to a mechanism for lactose/H+ symport by LacY: (i) LacY must be protonated to bind galactoside (the pK for binding is ~10.5). (ii) The limiting step for lactose/H+ symport in the absence of ∆µ̃H+ is deprotonation of Glu325, which has a pKa of ~10.5 by FTIR, whereas in the presence of ∆µ̃H+, the limiting step is opening of apo LacY on the other side of the membrane after dissociation of the sugar and deprotonation. (iii) Galactoside binding and dissociation--not ∆µ̃H+--are the driving force for alternating access. (iv) Galactoside binding involves induced fit causing transition to an occluded intermediate that mediates alternating access. (v) Galactoside dissociates, releasing the energy of binding. (vi) Arg302 comes into proximity with protonated Glu325 causing deprotonation. Accumulation of galactoside against a concentration gradient does not involve a change in KD on either side of the membrane, but the rate of deprotonation increases markedly. Thus, transport is driven chemiosmotically, but contrary to expectation, ∆µ̃H+ acts kinetically to control the rate of the process.
Awards/Honors:
2016 Honoree, 80th Birthday Symposium, NIH, Bethesda, Md
2014 Inducted into the Hall of Fame, Overbrook High School Alumni Association, Philadelphia, PA
2013 Storer Lectures, University of California Davis
2012 Provost's Lecture, Kansas State University, Manhattan, KA
2012 The Peter Mitchell Medal, European Bioenergetics Congress
2012 Louis Nahum Lecture, Yale University, New Haven, CT
2009 Distinguished Alumni Achievement Award, Haverford College
2009 First Presidential Distinguished Lecture, Texas Tech Univ. Health Sciences Center, Lubbock, TX.
2008 Philip Handler Memorial Lecture, Duke University
2008 Elected Fellow, American Association for the Advancement of Science
2007 Anatrace Membrane Protein Award, Biophysical Society, Long Beach, CA
2005 Koepe Memorial Lecture, Oklahoma State University, Stillwater, OK
2004 George Connell Guest Lecture, University of Toronto, Toronto, Ontario, Canada
2004 Speaker, Joseph F. Hoffman Symposium on Membrane Biology, Yale University, New Haven, CT
2004 Speaker and Honoree as the 2nd “Coleman Fellow in Life Sciences,” Noun Shavit Memorial Lecture Fund, Ben-Gurion University, Beer-Sheva, Israel
2003 Plenary Lecturer, RIKEN/BBSRC Joint Symposium at Spring-8, Japan- UK Membrane Protein Structure Biology Symposium, Osaka, Japan
2003 Speaker, Nobel Symposium “Membrane Proteins: Structure, Function and Assembly,” Sweden
2002 Rosetta Briegel Barton Lecture, University of Oklahoma, Norman, OK
2002 Peter F. Curran Lecture, Yale University, New Haven, CT
2002 Symposium Chairman and Speaker, 44th Annual Biophysical Society Meeting, New Orleans
2001 Speaker, 18th International Congress of Biochemistry and Molecular Biology, “Beyond the Genome,” Birmingham, England
2000 Speaker. Commemoration of the 25th Anniversary of Bioenergetics, Tokyo, Japan
1998 Speaker, Symposium Celebrating the Rededication of the Department of Cellular and Molecular Physiology at Yale University School of Medicine
1997 Elected Fellow of American Academy of Microbiology
1997 Max Gruber Lecturer, University of Groningen, The Netherlands
1996 Mt. Sinai Medical School Dean's Lecture, Mt. Sinai School of Medicine
1996 Honoree: "Molecular Mechanism of Energy Coupling in Transport Systems," Honoring 60th birthday and Lifetime Achievement," Villefranche-sur-Mére, France
1996 Distinguished Lecture, Robert Wood Johnson Medical School
1993 3M Life Sciences Award (shared with Dr. Peter C. Nowell)
1993 University of Helsinki Medal and Special Lecture, Helsinki, Finland
1993 Harold Lamport Lecture, College of Physicians and Surgeons, Columbia University
1993 Chairman, Gordon Conference on Transport
1991 Oak Ridge National Laboratory Scientific Advisory Committee
1991-1992 Chairman, Board of Scientific Counselors of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDKD)
1987-1991 Board of Scientific Counselors of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDKD)
1989 George A. Feigen Memorial Lecture, Stanford University
1989 Philips Lecturer, Haverford College
1988 Nathan Kaplan Memorial Lecturer, U. C. San Diego
1988 Harvey Lecturer
1988 Albert Einstein Distinguished Alumnus Award
1988 Kenneth Cole Award, American Biophysical Society
1987 Welcome Visiting Professor, University of Idaho, Moscow, ID
1987 Elected Member, National Academy of Sciences
1986 Elected Fellow, American Academy of Arts and Sciences
1981 Albert Alberman Visiting Professor, Technion-Israel Institute of Technology, Haifa, Israel
1980 Lady Davis Visiting Professorship, The Hebrew University, Jerusalem, Israel
1974 Third Annual Lewis Rosenstiel Award, Brandies University
1974 Battelle Memorial Foundation Fellow, Seattle, WA 1973
1973 Selman A. Waksman Honorary Lectureship Award, Theobold Smith Society, NJ Branch, American Society for Microbiology
1963-1964 Edward John Noble Foundation Fellow