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Modeling of Biomolecular Systems Interactions, Dynamics, and Allostery Session I Abstracts
Distinguishing between Allosteric Mechanisms Using Structural Mass-Spectrometry Is
Demonstrated for the Chaperonin GroEL
Amnon Horovitz
.
Weizmann Institute of Science, Rehovot, Israel.
Allosteric regulation is often described by the concerted Monod–Wyman–Changeux or
sequential Koshland–Némethy–Filmer models of cooperativity. In general, however, it has been
impossible to distinguish between these allosteric models using ensemble measurements of
ligand binding in bulk protein solutions. In this talk, a new structural mass-spectrometry
approach will be described that breaks this impasse by providing the full distribution of ligand-
bound states of a protein complex. Given this distribution, it is possible to determine all the
binding constants of a ligand to a highly multimeric cooperative system and, thus, infer its
allosteric mechanism. The approach will be demonstrated for the chaperonin GroEL that consists
of two back-to-back stacked heptameric rings with a cavity at each end where protein folding can
take place. GroEL displays intra-ring positive cooperativity and inter-ring negative cooperativity
in ATP binding, with respect to ATP, that are crucial for its function. It will be shown that this
new approach provides evidence for a concerted mechanism of allosteric switching and
information on the ATP-loading pathway. The impact of the concerted nature of the intra-ring
allosteric transitions of GroEL on its folding function will be discussed.
Ras: a Structural Biologist View and Questions
Ruth Nussinov
.
NCI, Frederick, MD, USA.
Ras proteins are small GTPases that act as signal transducers between cell surface receptors and
several intracellular signaling cascades. KRas4B is among the frequently mutated oncogenes in
human tumors. Ras proteins consist of highly homologous catalytic domains, and flexible C-
terminal hypervariable regions (HVRs) that differ significantly across Ras isoforms. We have
been focusing on key mechanistic questions in Ras biology from the structural standpoint. These
include whether Ras forms dimers, and if so what is their structural landscape; how do Ras
dimers activate Raf, a key Ras effector in a major signaling pathway; how calmodulin inhibit Raf
signaling, and the potential role of the hypervariable region and its membrane anchoring
regulation. We believe that structural biology, computations and experiment, are uniquely able to
tackle these fascinating questions.
