Department of Pharmaceutical Chemistry , University of California San Francisco , San Francisco , California 94158 , United States.
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , Stanford University , Menlo Park , California 94025 , United States.
J Am Chem Soc. 2018 May 30;140(21):6518-6521. doi: 10.1021/jacs.8b02100. Epub 2018 May 18.
Catalytic modules of assembly-line polyketide synthases (PKSs) have previously been observed in two very different conformations-an "extended" architecture and an "arch-shaped" architecture-although the catalytic relevance of neither has been directly established. By the use of a fully human naïve antigen-binding fragment (F) library, a high-affinity antibody was identified that bound to the extended conformation of a PKS module, as verified by X-ray crystallography and tandem size-exclusion chromatography-small-angle X-ray scattering (SEC-SAXS). Kinetic analysis proved that this antibody-stabilized module conformation was fully competent for catalysis of intermodular polyketide chain translocation as well as intramodular polyketide chain elongation and functional group modification of a growing polyketide chain. Thus, the extended conformation of a PKS module is fully competent for all of its essential catalytic functions.
尽管尚未直接确定这两种构象中的任何一种在催化上的相关性，但此前已在两种截然不同的构象中观察到了装配线聚酮合酶 (PKS) 的催化模块 - “延伸”构象和“拱形”构象。通过使用完全人源天然抗原结合片段 (F) 文库，鉴定出一种高亲和力的抗体，该抗体与 PKS 模块的延伸构象结合，这一点通过 X 射线晶体学和串联尺寸排阻色谱-小角 X 射线散射 (SEC-SAXS) 得到了验证。动力学分析证明，这种抗体稳定的模块构象完全有能力催化模块间聚酮链易位以及模块内聚酮链延伸和生长聚酮链的功能基团修饰。因此，PKS 模块的延伸构象完全有能力执行其所有基本的催化功能。
