The chitinase-like proteins YKL-39 (chitinase 3-like-2) and YKL-40 (chitinase 3-like-1) are highly expressed in a number of human cells independent of their origin (mesenchymal, epithelial or haemapoietic). Elevated serum levels of YKL-40 have been associated with a negative outcome in a number of diseases ranging from cancer to inflammation and asthma. YKL-39 expression has been associated with osteoarthritis. However, despite the reported association with disease, the physiological or pathological role of these proteins is still very poorly understood. Although YKL-39 is homologous to the two family 18 chitinases in the human genome, it has been reported to lack any chitinase activity. In the present study, we show that human YKL-39 possesses a chitinase-like fold, but lacks key active-site residues required for catalysis. A glycan screen identified oligomers of N-acetylglucosamine as preferred binding partners. YKL-39 binds chitooligosaccharides and a newly synthesized derivative of the bisdionin chitinase-inhibitor class with micromolar affinity, through a number of conserved tryptophan residues. Strikingly, the chitinase activity of YKL-39 was recovered by reverting two non-conservative substitutions in the active site to those found in the active enzymes, suggesting that YKL-39 is a pseudo-chitinase with retention of chitinase-like ligand-binding properties.
几丁质酶样蛋白 YKL-39(
几丁质酶 3-like-2)和 YKL-40(
几丁质酶 3-like-1)在许多人体细胞中高度表达,与细胞来源(间质、上皮或造血)无关。血清中 YKL-40
水平的升高与癌症、炎症和哮喘等多种疾病的不良后果有关。YKL-39 的表达与骨关节炎有关。然而,尽管有报道称这些蛋白与疾病有关,但人们对它们的生理或病理作用仍然知之甚少。虽然 YKL-39 与人类
基因组中的两个 18 族
几丁质酶同源,但据报道它缺乏任何
几丁质酶活性。在本研究中,我们发现人类 YKL-39 具有类似
几丁质酶的折叠,但缺乏催化所需的关键活性位点残基。通过聚糖筛选发现,N-乙酰
葡糖胺寡聚体是首选的结合伙伴。YKL-39 通过一些保守的色
氨酸残基与壳
寡糖和一种新合成的双二
酮类几丁质酶抑制剂衍
生物结合,具有微摩尔亲和力。令人震惊的是,通过将活性位点中的两个非保守取代恢复到活性酶中的取代,YKL-39 的
几丁质酶活性得以恢复,这表明 YKL-39 是一种假
几丁质酶,保留了类似
几丁质酶的
配体结合特性。