CEA, iBiTec-S, Service d'Ingénierie Moléculaire des Protéines, Laboratoire de Toxinologie Moléculaire et Biotechnologies, Gif-sur-Yvette F-91191, France.
J Mol Biol. 2011 Dec 9;414(4):530-44. doi: 10.1016/j.jmb.2011.10.007. Epub 2011 Oct 20.
Human prostate-specific antigen (PSA or human kallikrein-related peptidase 3) present in small quantities in the sera of healthy men becomes elevated in prostate cancer (PCa) and other prostate disorders. The ability to identify the free PSA fraction associated with PCa could increase the reliability of the PSA diagnostic test. Here we present the crystal structure of human PSA from seminal fluid in a sandwich complex with two monoclonal antibodies (mAbs). MAb 5D5A5 captures total PSA with exceptionally high affinity, and mAb 5D3D11 selectively discriminates between free PSA subforms that are more abundant in sera from patients with PCa. Although the antigen is not of seric origin, several insights into cancer diagnosis can be discerned from this complex. MAb 5D3D11 recognizes a PSA conformation different from that previously reported. Interacting with the kallikrein loop, the PSA N-linked glycan attached to asparagine 61 is an uncommonly complex sialated triantennary chain. O-linked glycosylation is observed at threonine 125. The description of how PSA subforms in prostatic fluid can be discriminated using pairs of antibodies is a first step in the design of new strategies that are capable of real discrimination among PSA subforms, which will lead to the formulation of more reliable diagnostic tests. In a companion article [Muller, B. H., Savatier, A., L'Hostis, G., Costa, N., Bossus, M., Michel, S., et al. (2011). In vitro affinity maturation of an anti-PSA antibody for prostate cancer diagnostic assay. J. Mol. Biol.], we describe engineering efforts to improve the affinity of mAb 5D3D11, a first step towards such goal.
人前列腺特异性抗原（PSA 或人激肽释放酶相关肽 3）在健康男性血清中含量很少，但在前列腺癌（PCa）和其他前列腺疾病中会升高。能够识别与 PCa 相关的游离 PSA 片段可以提高 PSA 诊断测试的可靠性。在这里，我们展示了来自精液的人 PSA 的晶体结构，它与两种单克隆抗体（mAb）形成三明治复合物。mAb 5D5A5 以极高的亲和力捕获总 PSA，而 mAb 5D3D11 则选择性地区分在来自 PCa 患者的血清中更为丰富的游离 PSA 亚基。尽管抗原不是血清来源的，但从这个复合物中可以看出一些癌症诊断的见解。mAb 5D3D11 识别到与之前报道的不同的 PSA 构象。与激肽环相互作用，与天冬酰胺 61 连接的 PSA N-连接聚糖是一种罕见的复杂唾液酸三触角链。在苏氨酸 125 处观察到 O-连接糖基化。描述如何使用抗体对前列腺液中的 PSA 亚基进行区分是设计能够真正区分 PSA 亚基的新策略的第一步，这将导致制定更可靠的诊断测试。在一篇配套文章[Muller, B. H., Savatier, A., L'Hostis, G., Costa, N., Bossus, M., Michel, S., et al. (2011). In vitro affinity maturation of an anti-PSA antibody for prostate cancer diagnostic assay. J. Mol. Biol.]中，我们描述了为提高 mAb 5D3D11 的亲和力而进行的工程努力，这是实现这一目标的第一步。
