Conformational analysis of the Streptococcus pneumoniae hyaluronate lyase and characterization of its hyaluronan-specific carbohydrate-binding module [Protein Structure and Folding]
August 6th, 2014 by Suits, M. D. L., Pluvinage, B., Law, A., Liu, Y., Palma, A. S., Chai, W., Feizi, T., Boraston, A. B.
For a subset of pathogenic microorganisms, including Streptococcus pneumoniae, the recognition and degradation of host hyaluronan contributes to bacterial spreading through the extracellular matrix and enhancing access to host-cell surfaces. The hyaluronate lyase, Hyl, presented on the surface of S. pneumoniae performs this role. Using glycan microarray screening, affinity electrophoresis, and isothermal titration calorimetry we show that the N-terminal module of Hyl is a hyaluronan-specific carbohydrate-binding module (CBM) and the founding member of CBM family 70. The 1.2 Å resolution X-ray crystal structure of CBM70 revealed it to have a β-sandwich fold similar to other CBMs. The electrostatic properties of the binding site, which was identified by site-directed mutagenesis, are distinct from other CBMs and complementary to its acidic ligand, hyaluronan. Dynamic light scattering and solution small-angle X-ray scattering (SAXS) revealed the full-length Hyl protein to exist as a monomer-dimer mixture in solution. Through a detailed analysis of the SAXS data we report the pseudo-atomic solution structures of the monomer and dimer forms of the full-length multimodular Hyl.