Jam Murielle, Ficko-Blean Elizabeth, Labourel Aurore, Larocque Robert, Czjzek Mirjam, Michel Gurvan
Sorbonne Université, UPMC Univ Paris 06, CNRS, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, Roscoff Cedex, Bretagne, France.
FEBS J. 2016 May;283(10):1863-79. doi: 10.1111/febs.13707. Epub 2016 Mar 31.
Laminarin is an abundant brown algal storage polysaccharide. Marine microorganisms, such as Zobellia galactanivorans, produce laminarinases for its degradation, which are important for the processing of this organic matter in the ocean carbon cycle. These laminarinases are often modular, as is the case with ZgLamC which has an N-terminal GH16 module, a central family 6 carbohydrate-binding module (CBM) and a C-terminal PorSS module. To date, no studies have characterized a true marine laminarin-binding CBM6 with its natural carbohydrate ligand. The crystal structure of ZgLamCCBM6 indicates that this CBM has two clefts for binding sugar (variable loop site, VLS; and concave face site, CFS). The ZgLamCCBM6 VLS binds in an exo-manner and the CFS interacts in an endo-manner with laminarin. Isothermal titration calorimetry (ITC) experiments on native and mutant ZgLamCCBM6 confirm that these binding sites have different modes of recognition for laminarin, in agreement with the 'regional model' postulated for CBM6-binding modules. Based on ITC data and structural data, we propose a model of ZgLamCCBM6 interacting with different chains of laminarin in a multivalent manner, forming a complex cross-linked protein-polysaccharide network.
PDB code 5FUI.
海带多糖是一种丰富的褐藻储存多糖。海洋微生物，如食半乳糖海杆菌，会产生海带多糖酶来降解它，这对海洋碳循环中这种有机物的处理很重要。这些海带多糖酶通常是模块化的，食半乳糖海杆菌海带多糖酶C（ZgLamC）就是如此，它有一个N端糖基水解酶16（GH16）模块、一个中央6家族碳水化合物结合模块（CBM）和一个C端孔形成小蛋白样分泌系统（PorSS）模块。迄今为止，尚无研究对具有天然碳水化合物配体的真正海洋海带多糖结合CBM6进行表征。食半乳糖海杆菌海带多糖酶C的CBM6（ZgLamCCBM6）晶体结构表明，该CBM有两个用于结合糖的裂隙（可变环位点，VLS；和凹面位点，CFS）。ZgLamCCBM6的VLS以一种外切方式结合，而CFS以内切方式与海带多糖相互作用。对天然和突变型ZgLamCCBM6进行的等温滴定量热法（ITC）实验证实，这些结合位点对海带多糖具有不同的识别模式，这与为CBM6结合模块提出的“区域模型”一致。基于ITC数据和结构数据，我们提出了一个ZgLamCCBM6以多价方式与海带多糖不同链相互作用，形成复杂交联的蛋白质 - 多糖网络的模型。
PDB代码5FUI。
