Abstract
Helix pomatia agglutinin (HPA) is a N-acetylgalactosamine (GalNAc) binding lectin found in the albumen gland of the roman snail. As a constituent of perivitelline fluid, HPA protects fertilized eggs from bacteria and is part of the innate immunity system of the snail. The peptide sequence deduced from gene cloning demonstrates that HPA belongs to a family of carbohydrate-binding proteins recently identified in several invertebrates. This domain is also present in discoidin from the slime mold Dictyostelium discoideum. Investigation of the lectin specificity was performed with the use of glycan arrays, demonstrating that several GalNAc-containing oligosaccharides are bound and rationalizing the use of this lectin as a cancer marker. Titration microcalorimetry performed on the interaction between HPA and GalNAc indicates an affinity in the 10(-4) M range with an enthalpy-driven binding mechanism. The crystal structure of HPA demonstrates the occurrence of a new beta-sandwich lectin fold. The hexameric quaternary state was never observed previously for a lectin. The high resolution structure complex of HPA with GalNAc characterizes a new carbohydrate binding site and rationalizes the observed preference for alphaGalNAc-containing oligosaccharides.
Highlights
Helix pomatia agglutinin (HPA) is a N-acetylgalactosamine (GalNAc) binding lectin found in the albumen gland of the roman snail
In the edible roman snail, a lectin named Helix pomatia agglutinin (HPA)5 is secreted by the albumen gland that produces the perivitelline fluid, composed of protein and polysaccharide complexes that coat each fertilized egg [8]
The oligosaccharide target recognized by HPA on the surface of pathogens has not yet been identified, its specificity is close to that of tachylectin-2 that binds to GlcNAc and GalNAc and recognizes staphylococcal lipoteichoic acids and lipopolysaccharides from several Gramnegative bacteria [6]
Summary
The high resolution structure complex of HPA with GalNAc characterizes a new carbohydrate binding site and rationalizes the observed preference for ␣GalNAc-containing oligosaccharides Because of their ability to recognize complex carbohydrates on cell surfaces with high specificity, lectins are proteins that. In the edible roman snail, a lectin named Helix pomatia agglutinin (HPA) is secreted by the albumen gland that produces the perivitelline fluid, composed of protein and polysaccharide complexes that coat each fertilized egg [8] This lectin has the property to aggregate bacteria such as group C streptococci [9] and Listeria monocytogenes [10] and is able to bind to the surface of the herpesvirus [11]. 0.013 0.032 0.032 a R.m.s.d., root mean square deviation. b Angle distances and out of plane distances for SHELX refinement
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