D.Barathy
et al.
(2014).
New structural forms of a mycobacterial adenylyl cyclase Rv1625c.
Iucrj,
1,
338-348.
PubMed id: 25295175
DOI: 10.1107/S2052252514016741
New structural forms of a mycobacterial adenylyl cyclase Rv1625c.
D.Barathy,
R.Mattoo,
S.Visweswariah,
K.Suguna.
ABSTRACT
Rv1625c is one of 16 adenylyl cyclases encoded in the genome of Mycobacterium
tuberculosis. In solution Rv1625c exists predominantly as a monomer, with a
small amount of dimer. It has been shown previously that the monomer is active
and the dimeric fraction is inactive. Both fractions of wild-type Rv1625c
crystallized as head-to-head inactive domain-swapped dimers as opposed to the
head-to-tail dimer seen in other functional adenylyl cyclases. About half of the
molecule is involved in extensive domain swapping. The strain created by a
serine residue located on a hinge loop and the crystallization condition might
have led to this unusual domain swapping. The inactivity of the dimeric form of
Rv1625c could be explained by the absence of the required catalytic site in the
swapped dimer. A single mutant of the enzyme was also generated by changing a
phenylalanine predicted to occur at the functional dimer interface to an
arginine. This single mutant exists as a dimer in solution but crystallized as a
monomer. Analysis of the structure showed that a salt bridge formed between a
glutamate residue in the N-terminal segment and the mutated arginine residue
hinders dimer formation by pulling the N-terminal region towards the dimer
interface. Both structures reported here show a change in the dimerization-arm
region which is involved in formation of the functional dimer. It is concluded
that the dimerization arm along with other structural elements such as the
N-terminal region and certain loops are vital for determining the oligomeric
nature of the enzyme, which in turn dictates its activity.
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