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Crystal Structure of the Bacterial YhcH Protein Indicates a Role in Sialic Acid Catabolism

Alexey Teplyakov,^1* Galina Obmolova,^1, John Toedt,^1, Michael Y. Galperin,² and Gary L. Gilliland^1,

Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute and National Institute of Standards and Technology, Rockville, Maryland,¹ National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland²

Received 28 February 2005/ Accepted 11 May 2005

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-Å resolution by multiple-wavelength anomalous diffraction. The protein fold is a variation of the double-stranded ß-helix. Two antiparallel ß-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.

Present address: National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Md.

Present address: Department of Physical Science, Eastern Connecticut State University, Willimantic, Conn.

Present address: Centocor Inc., Radnor, Pa.