Vk. Shier et al., Identification of the active oligomeric state of an essential adenine DNA methyltransferase from Caulobacter crescentus, J BIOL CHEM, 276(18), 2001, pp. 14744-14751
Caulobacter crescentus contains one of the two known prokaryotic DNA methyl
transferases that lacks a cognate endonuclease. This endogenous cell cycle
regulated adenine DNA methyltransferase (CcrM) is essential for C, crescent
us cellular viability. DNA methylation catalyzed by CcrM, provides an oblig
atory signal for the proper progression through the cell cycle. To further
our understanding of the regulatory role played by CcrM, we sought to inves
tigate its biophysical properties, In this paper we employed equilibrium ul
tracentrifugation, velocity ultracentrifugation, and chemical cross-linking
to show that CcrM is dimeric at physiological concentrations. However, sur
face plasmon resonance experiments in the presence of S-adenosyl-homocystei
ne evince that CcrM binds as a monomer to a defined hemi-methylated DNA sub
strate containing the canonical methylation sequence, GANTC, Initial veloci
ty experiments demonstrate that dimerization of CcrM does not affect DNA me
thylation. Collectively, these findings suggest that CcrM is active as a mo
nomer and provides a possible in vivo role for dimerization as a means to s
tabilize CcrM from premature catabolism.