Structure of a plant cell wall fragment complexed to pectate lyase C
Structure of a plant cell wall fragment complexed to pectate lyase C
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DOI：
10.1105/tpc.11.6.1081
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发表时间：
1999-06-01
期刊：
影响因子：
11.6
通讯作者：
Jurnak, F
中科院分区：
文献类型：
--
作者：
Scavetta, RD;Herron, SR;Jurnak, F
果胶酸裂解酶C（PelC）R218 K突变体和植物细胞壁片段之间的复合物的三维结构已经通过X-射线衍射技术测定到2.2埃的分辨率，并精确到18.6%的晶体学R因子。（[1->4]-alpha-D-GalpA）（3）-（1->4）-D-GalpA，由5个通过α-（1->4）糖苷键连接的吡喃半乳糖醛酸糖单元（D-GalpA）组成，PelC由植物病原体欧文氏菌分泌，并在软腐病中降解植物细胞壁的果胶组分。通过使用失活的R218 K突变体将底物捕获在晶体中。底物的五个糖单元中有四个是有序的，代表了植物细胞壁中果胶酸组分的原子视图。果胶酸片段的构象是2（1）和3（1）右手螺旋的混合物，底物结合在裂缝中，主要与带正电荷的基团相互作用：PelC上的赖氨酸或精氨酸氨基酸或复合物中发现的四个Ca 2+离子。所观察到的蛋白质-寡糖相互作用为果胶酸裂解酶蛋白质家族中的许多不变和保守氨基酸提供了功能性解释。由于R218 K PelC-半乳糖醛酸五糖复合物代表了反应途径中的中间体，因此其结构也揭示了有关酶促机制的重要细节。值得注意的是，结果表明，精氨酸，这是不变的果胶酸裂解酶超家族，是在β消除裂解的聚半乳糖醛酸的质子提取启动的氨基酸。
The three-dimensional structure of a complex between the pectate lyase C (PelC) R218K mutant and a plant cell wall fragment has been determined by x-ray diffraction techniques to a resolution of 2.2 Angstrom and refined to a crystallographic R factor of 18.6%, The oligosaccharide substrate, alpha-D-GalpA-([1-->4]-alpha-D-GalpA)(3)-(1-->4)-D-GalpA, is composed of five galacturonopyranose units (D-GalpA) linked by alpha-(1-->4) glycosidic bonds, PelC is secreted by the plant pathogen Erwinia chrysanthemi and degrades the pectate component of plant cell walls in soft rot diseases. The substrate has been trapped in crystals by using the inactive R218K mutant. Four of the five saccharide units of the substrate are well ordered and represent an atomic view of the pectate component in plant cell walls. The conformation of the pectate fragment is a mix of 2(1) and 3(1) right-handed helices, The substrate binds in a cleft, interacting primarily with positively charged groups: either lysine or arginine amino acids on PelC or the four Ca2+ ions found in the complex. The observed protein-oligosaccharide interactions provide a functional explanation for many of the invariant and conserved amino acids in the pectate lyase family of proteins. Because the R218K PelC-galacturonopentaose complex represents an Intermediate in the reaction pathway, the structure also reveals important details regarding the enzymatic mechanism. Notably, the results suggest that an arginine, which is invariant in the pectate lyase superfamily, is the amino acid that initiates proton abstraction during the beta elimination cleavage of polygalacturonic acid.