Structures of Streptococcus pneumoniae Hyaluronate Lyase in Complex with Chondroitin and Chondroitin Sulfate Disaccharides

Abstract

Streptococcus pneumoniae hyaluronate lyase is a surface enzyme of this Gram-positive bacterium. The enzyme degrades hyaluronan and chondroitin/chondroitin sulfates by cleaving the ␤1,4-glycosidic linkage between the glycan units of these polymeric substrates. This degradation helps spreading of this bacterial organism throughout the host tissues and facilitates the disease process caused by pneumococci. The mechanism of this degradative process is based on ␤-elimination, is termed proton acceptance and donation, and involves selected residues of a well defined catalytic site of the enzyme. The degradation of hyaluronan alone is thought to proceed through a processive mode of action. The structures of complexes between the enzyme and chondroitin as well as chondroitin sulfate disaccharides allowed for the first detailed insights into these interactions and the mechanism of action on chondroitins. This degradation of chondroitin/chondroitin sulfates is nonprocessive and is selective for the chondroitin sulfates only with certain sulfation patterns. Chondroitin sulfation at the 4-position on the nonreducing site of the linkage to be cleaved or 2-sulfation prevent degradation due to steric clashes with the enzyme. Evolutionary studies suggest that hyaluronate lyases evolved from chondroitin lyases and still retained chondroitin/chondroitin sulfate degradation abilities while being specialized in the degradation of hyaluronan. The more efficient processive degradation mechanism has come to be preferred for the unsulfated substrate hyaluronan.

Unusual Structural Features of the Bacteriophage-associated Hyaluronate Lyase (hylp2)

“…The phage H4489A and S. hyalurolyticus hyaluronate lyases have strict specificity for HA, not cleaving chondroitins of any kind (29,30), whereas SpnHL and SagHL not only processes HA but certain CS also (33). To study the kinetic properties of enzymatic reaction as well as substrate specificity, a comparative analysis of the kinetic properties of the full-length protein, the N:C complex, and the isolated C-terminal domain using HA and CS as substrates were carried out and summarized in Fig.…”

Versatility of pneumococcal surface proteins

“…The hyaluronate lyase (Hyl), which primarily hydrolyses hyaluronan, is a four-domain enzyme consisting of an N-terminal carbohydrate domain, followed by a spacer domain, the helical barrel-like catalytic domain, and finally the C-terminal domain (Rigden & Jedrzejas, 2003). hyl knockout mutants are attenuated in an intraperitoneal mouse infection model (Chapuy-Regaud et al, 2003), but the precise function of Hyl during pathogenesis has yet to be clarified.…”

Insight into the Role of Substrate-binding Residues in Conferring Substrate Specificity for the Multifunctional Polysaccharide Lyase Smlt1473

“…Despite diverse substrate specificity, secondary structure content, and tertiary folds, this three-step mechanism is highly conserved across the 23 different polysaccharide lyase families (PL-1 to PL-23) (2, 3) and can be divided into two general categories as follows: metal ion-assisted and metal ion-independent lyases, the latter of which utilize nearby arginine, asparagine, or glutamine residues for substrate neutralization with a highly conserved tyrosine or histidine acting as the base and tyrosine as the acid (3). A consensus has not been met regarding the specific roles of the catalytic histidine and tyrosine, namely whether tyrosine acts as proton acceptor and donor with histidine stabilizing an intermediate, the mechanism proposed for alginate lyases (4) and xanthan lyases (5), or whether histidine acts as the proton acceptor and tyrosine as the proton donor, the mechanism proposed for hyaluronan lyases (6,7). Furthermore, Shaya et al (8) proposed a third mechanism for heparinase II in which the residue responsible □ S This article contains supplemental Table S1.…”