Carbohydtare structure of prostate specific antigen (PSA)

血清前列腺特异性抗原(PSA)检测被广泛用于前列腺癌(PC)的检测。由于PSA不是癌症特异性的，而是前列腺特异性的，常规的血清PSA检测无法避免假阳性诊断。为了将肿瘤相关碳水化合物的改变应用于PSA检测的改进，我们首先阐明了从人精液中纯化的PSA的N-糖链的结构特征。精液PSA中N-糖链的核心结构为复合型双触角低聚糖，与文献报道的结构一致。然而，我们在精液α上发现唾液酸PSA2-3半乳糖连接作为附加的末端碳水化合物结构。用凝集素亲和层析法分析了PC和良性前列腺增生症(BPH)患者血清PSA的糖基组成。用凝集素亲和柱层析、总PSA和游离PSA检测凝集素结合活性。测定了刀豆蛋白A(ConA)、豆角凝集素(Lch)、金银花凝集素(AAL)、接骨木凝集素(SNA)和山木凝集素(MAA)与PSA上的碳水化合物的结合亲和力。在所检测的凝集素中，PC和BPH患者的游离血清PSA的MAA结合比例显示出最显著的差异。表面等离子体共振(SPR)分析也证实了PSA与MAA的结合。提示前列腺癌与良性前列腺增生症患者血清中游离PSA与MAA凝集素具有明显的亲和力，可作为诊断前列腺癌的潜在指标。

Serum prostate specific antigen (PSA) assay is widely used for detection of prostate cancer (PC). Since PSA is not cancer-specific but prostate-specific, false positive diagnosis cannot be avoided by the conventional serum PSA test. In order to apply the cancer-associated carbohydrate alteration to the improvement of PSA assay, we first elucidated the structural characteristics of the N-glycans of PSA purified from human seminal fluid. The predominant core structure of N-glycan of seminal fluid PSA was a complex type biantennary oligosaccharide and was consistent with the structure reported previously. However, we found the sialic acid α2-3 galactose linkage as an additional terminal carbohydrate structure on seminal fluid PSA. We then analyzed the carbohydrate moiety of serum PSA from the patients with PC and benign prostate hypertrophy (BPH) using lectin affinity chromatography. Lectin binding activity was assessed by lectin affinity column chromatography followed by total and free PSA assay. Concanavalin A (Con A), Lens culinaris (LcH), Aleuria aurantia (AAL), Sambucus nigra (SNA), and Maackia amurensis (MAA) lectins were tested for their binding affinity to the carbohydrates on PSA. Among the lectins examined, the MAA-bound fraction of free serum PSA showed the most significant difference between PC and BPH patients. The binding of PSA to MAA was also confirmed by surface plasmon resonance (SPR) analysis. These results suggested that the distinct binding affinity of free serum PSA to MAA lectin between PC and BPH could be a potential measure for diagnosing PC.