Page 10 - U. Protein structure and function

[U. Protein structure and function-5]

Solution structure of the nucleotide hydrolase BlsM:

importance of its substrate specificity

Minhee Kang¹˙², Zhengrong Wu¹˙*

¹Chemistry, The Ohio State University, Columbus 43212, USA, ²Pharmacy, Korea University, Sejong 30019, S. Korea

Biosynthesis of the peptidyl nucleoside antifungal agent blasticidin S in Streptomyces griseochromogenes requires
the hydrolytic function of a nucleotide N-glycosidase, BlsM, to provide free cytosine from CMP. BlsM belongs to a
new family of nucleotide hydrolases that specifically act on CMP or dCMP without transferase activity. BlsM also

has a novel cytidine deaminase activity, converting cytidine to uridine.

The solution structure of BlsM was determined by multi-dimensional NMR to gain insight into the substrate

specificity and dual function. BlsM is a symmetric homodimer, and each monomer consists of a five-parallel β-sheet
sandwiched by five α-helixes. The structure shows a confined active site close to the domain interface enclosed by

conserved hydrophobic residues. This active site is smaller than that of a purine nucleotide hydrolase, RCL, which
is consistent with its substrate specificity for a pyrimidine. Phe19 interacts with 2’-OH of CMP controlling optimal

positioning the ribose. Upon F19Y mutation, the steric clash between the –OH of the tyrosine and the 2’-OH of
CMP potentially alters the substrate orientation reversing substrate specificity to the dCMP. Interestingly, with

impaired hydrolytic activity, the F19Y mutant exhibited a deaminase activity on CMP.