Background: Hyl from Streptococcus pneumoniae degrades host hyaluronan, an important polysaccharide component of the mammalian extracellular matrix. Results: Hyl has a hyaluronan-specific carbohydrate-binding module, an extended conformation, and a propensity to dimerize. Conclusion: Hyl both binds and degrades hyaluronan, which is facilitated by its cell surface presentation. Significance: This is the first structural and functional characterization of a glycosaminoglycan-specific carbohydrate-binding module. 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 revealed the full-length Hyl protein to exist as a monomer/dimer mixture in solution. Through a detailed analysis of the small angle x-ray scattering data, we report the pseudoatomic solution structures of the monomer and dimer forms of the full-length multimodular Hyl.
【저자키워드】 Crystallography, glycobiology, Hyaluronan, carbohydrate, Streptococcus, carbohydrate-binding protein, Carbohydrate Processing, Small Angle X-ray Scattering (SAXS), Hyaluronate Lyase,