The f
irst structure of a glycerol k
inase from a Gram-pos
it
ive organ
ism,
Enterococcuscasseliflavus, has been determ
ined to 2.8 &Ar
ing; resolut
ion
in the presence of glycerol and to 2.5 &Ar
ing; resolut
ion
in the absence of substrate. The substrate-
induced closure of 7
images/ent
it
ies/deg.g
if">
is s
ign
if
icantly smaller than that reportedfor hexok
inase, a model for substrate-med
iated doma
in closure that has been proposed for glycerol k
inase.Desp
ite the 78% level of sequence
ident
ity and conformat
ional s
im
ilar
ity
in the catalyt
ic cleft reg
ions ofthe
En. casseliflavus and
Escherichia coli glycerol k
inases, remarkable structural d
ifferences have nowbeen
ident
if
ied. These d
ifferences correlate well w
ith the
ir d
ivergent regulatory schemes of act
ivat
ion byphosphorylat
ion
in
En. casseliflavus and alloster
ic
inh
ib
it
ion
in
E. coli. On the bas
is of our structuralresults, we propose a mechan
ism by wh
ich the phosphorylat
ion of a h
ist
idyl res
idue located 25 &Ar
ing; fromthe act
ive s
ite results
in a 10-15-fold
increase
in the act
iv
ity of the enterococcal glycerol k
inase.