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，因此常规血清PSA检测无法避免假阳性诊断。为了将肿瘤相关糖的改变应用于PSA检测方法的改进，我们首先阐明了从人精液中纯化的PSA的N-聚糖的结构特征。精浆PSA N-聚糖的主要核心结构为复合型双触角寡糖，与文献报道的结构一致。然而，我们发现唾液酸α2-3半乳糖键是精液PSA上额外的末端糖结构。然后我们用凝集素亲和层析法分析了PC和良性前列腺肥大（BPH）患者血清PSA中的碳水化合物部分。凝集素结合活性通过凝集素亲和柱色谱法，然后通过总PSA和游离PSA测定来评估。检测伴刀豆球蛋白A（ConA）、小透镜（LcH）、桔粉虱（AAL）、接骨木（SNA）和怀槐（MAA）凝集素与PSA上的碳水化合物的结合亲和力。在检查的凝集素中，游离血清PSA的MAA结合分数在PC和BPH患者之间显示出最显著的差异。PSA与MAA的结合也通过表面等离子体共振（SPR）分析证实。结果提示，血清PSA与MAA凝集素的特异性结合可作为诊断前列腺癌的一种新方法。

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.