多形類桿菌是人體腸道菌群中的主要成員之一,，它是一類典型的多糖采集菌,。多形類桿菌18%的基因組針對多糖的分解和利用。左圖左上角代表這種微生物的淀粉利用系統(tǒng)（SUS）,，它是由糖苷酶,，多糖蛋白的識別，以及運(yùn)輸?shù)鞍讟?gòu)成的,；右下角是Koropatkin等學(xué)者描述的SusD結(jié)構(gòu),，它通過識別淀粉的螺旋結(jié)構(gòu)與多糖結(jié)合。
人體的腸道中微生物可以執(zhí)行一些不用基因組編碼的功能,，包括分解不能消化的膳食多聚糖,。根據(jù)腸道菌群的處理能力,，經(jīng)過糖分解細(xì)菌的基因組分析可以確定了一些特定的多聚糖,，研究這些多聚糖的輸入和分解有助于人們確定其相關(guān)蛋白質(zhì)的結(jié)構(gòu)。在7月9日的《結(jié)構(gòu)》（Structure）雜志上,，Koropatkin等人描述了多形類桿菌結(jié)合,、分解淀粉所涉及的一個(gè)蛋白質(zhì)（SusD）的結(jié)構(gòu)。這種獨(dú)特的α-螺旋蛋白質(zhì)包含一個(gè)弧形的芳香殘基,，它可以補(bǔ)充淀粉的天然螺旋結(jié)構(gòu),，從而使這種構(gòu)象可以有效地與麥芽七糖結(jié)合。此外,，它還能夠以強(qiáng)于線性結(jié)構(gòu)的親和力與環(huán)狀低聚糖結(jié)合,。
幾個(gè)SusD蛋白質(zhì)-低聚糖的復(fù)合物表明，可能有一種內(nèi)在的識別配體的彈性結(jié)構(gòu),，這種結(jié)構(gòu)是由低聚糖的三維空間構(gòu)象決定的,，而不與復(fù)合糖的相互作用有關(guān)。（生物谷Bioon.com）
生物谷推薦原始出處：
Structure,，Vol 16, 1105-1115, 09 July 2008,，Nicole M. Koropatkin, Thomas J. Smith
Starch Catabolism by a Prominent Human Gut Symbiont Is Directed by the Recognition of Amylose Helices
Nicole M. Koropatkin,1 Eric C. Martens,2 Jeffrey I. Gordon,2 and Thomas J. Smith1,
1 Donald Danforth Plant Science Center, St. Louis, MO 63132, USA
2 Center for Genome Sciences, Washington University in St. Louis School of Medicine, St. Louis, MO 63108, USA
Corresponding author
Thomas J. Smith
[email protected]
Summary
The human gut microbiota performs functions that are not encoded in our Homo sapiens genome, including the processing of otherwise undigestible dietary polysaccharides. Defining the structures of proteins involved in the import and degradation of specific glycans by saccharolytic bacteria complements genomic analysis of the nutrient-processing capabilities of gut communities. Here, we describe the atomic structure of one such protein, SusD, required for starch binding and utilization by Bacteroides thetaiotaomicron, a prominent adaptive forager of glycans in the distal human gut microbiota. The binding pocket of this unique α-helical protein contains an arc of aromatic residues that complements the natural helical structure of starch and imposes this conformation on bound maltoheptaose. Furthermore, SusD binds cyclic oligosaccharides with higher affinity than linear forms. The structures of several SusD/oligosaccharide complexes reveal an inherent ligand recognition plasticity dominated by the three-dimensional conformation of the oligosaccharides rather than specific interactions with the composite sugars.
