Sanchez Jean-Frederic, Lescar Julien, Chazalet Valérie, Audfray Aymeric, Gagnon Jean, Alvarez Richard, Breton Christelle, Imberty Anne, Mitchell Edward P
Centre de Recherches sur les Macromolécules Végétales, CNRS, Université Joseph Fourier, 38041 Grenoble, France.
J Biol Chem. 2006 Jul 21;281(29):20171-80. doi: 10.1074/jbc.M603452200. Epub 2006 May 16.
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.
罗马蜗牛凝集素（HPA）是一种在罗马蜗牛蛋白腺中发现的与N - 乙酰半乳糖胺（GalNAc）结合的凝集素。作为卵周液的组成部分，HPA可保护受精卵免受细菌侵害，是蜗牛先天免疫系统的一部分。从基因克隆推导的肽序列表明，HPA属于最近在几种无脊椎动物中鉴定出的碳水化合物结合蛋白家族。该结构域也存在于黏菌盘基网柄菌的盘状菌素中。利用聚糖阵列对凝集素特异性进行了研究，结果表明几种含GalNAc的寡糖与之结合，这也解释了该凝集素作为癌症标志物的用途。对HPA与GalNAc之间相互作用进行的滴定微量热法表明，其亲和力在10^(-4) M范围内，结合机制为焓驱动。HPA的晶体结构表明出现了一种新的β-三明治凝集素折叠。此前从未在凝集素中观察到六聚体四级结构。HPA与GalNAc的高分辨率结构复合物表征了一个新的碳水化合物结合位点，并解释了观察到的对含αGalNAc寡糖的偏好。
