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2016 ; 291
(40
): 20900-20910
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Mechanistic Basis of Glutaminase Activation: A KEY ENZYME THAT PROMOTES GLUTAMINE
METABOLISM IN CANCER CELLS
#MMPMID27542409
Li Y
; Erickson JW
; Stalnecker CA
; Katt WP
; Huang Q
; Cerione RA
; Ramachandran S
J Biol Chem
2016[Sep]; 291
(40
): 20900-20910
PMID27542409
show ga
Glutamine-derived carbon becomes available for anabolic biosynthesis in cancer
cells via the hydrolysis of glutamine to glutamate, as catalyzed by GAC, a splice
variant of kidney-type glutaminase (GLS). Thus, there is significant interest in
understanding the regulation of GAC activity, with the suggestion being that
higher order oligomerization is required for its activation. We used x-ray
crystallography, together with site-directed mutagenesis, to determine the
minimal enzymatic unit capable of robust catalytic activity. Mutagenesis of the
helical interface between the two pairs of dimers comprising a GAC tetramer
yielded a non-active, GAC dimer whose x-ray structure displays a stationary loop
("activation loop") essential for coupling the binding of allosteric activators
like inorganic phosphate to catalytic activity. Further mutagenesis that removed
constraints on the activation loop yielded a constitutively active dimer,
providing clues regarding how the activation loop communicates with the active
site, as well as with a peptide segment that serves as a "lid" to close off the
active site following substrate binding. Our studies show that the formation of
large GAC oligomers is not a pre-requisite for full enzymatic activity. They also
offer a mechanism by which the binding of activators like inorganic phosphate
enables the activation loop to communicate with the active site to ensure maximal
rates of catalysis, and promotes the opening of the lid to achieve optimal
product release. Moreover, these findings provide new insights into how other
regulatory events might induce GAC activation within cancer cells.