The yhcH gene is part of the nan operon in bacteria that encodes proteins
involved in sialic acid catabolism. Determination of the crystal structure of
YhcH from Haemophilus influenzae was undertaken as part of a structural genomics
effort in order to assist with the functional assignment of the protein. The
structure was determined at 2.2-A resolution by multiple-wavelength anomalous
diffraction. The protein fold is a variation of the double-stranded beta-helix.
Two antiparallel beta-sheets form a funnel opened at one side, where a putative
active site contains a copper ion coordinated to the side chains of two
histidine and two carboxylic acid residues. A comparison to other proteins with
a similar fold and analysis of the genomic context suggested that YhcH may be a
sugar isomerase involved in processing of exogenous sialic acid.
