Simmer James P, Hu Jan C C
University of Texas Health Science Center at San Antonio, Department of Pediatric Dentistry, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
Connect Tissue Res. 2002;43(2-3):441-9. doi: 10.1080/03008200290001159.
Proteinases serve two important functions during dental enamel formation: They (a) process and (b) degrade enamel proteins. Different enzymes carry out these functions. Enamelysin (MMP-20) is the foremost enamel matrix-processing enzyme. Its expression initiates prior to the onset of dentin mineralization and continues throughout the secretory stage of amelogenesis. In vitro, enamelysin catalyzes all of the amelogenin cleavages that are known to occur during the secretory stage in vivo, and it is probably the enzyme responsible for the processing of all enamel proteins. There is evidence suggesting that enamelysin activity is critical for proper enamel formation. Uncleaved and processed enamel proteins often segregate into different compartments within the developing enamel layer, suggesting that they may have different functions. Intact ameloblastin and its C-terminal cleavage products localize in the superficial rod and interrod enamel, while its N-terminal cleavage products congregate in the sheath space. Intact enamelin is only present at the mineralization front within a micrometer of the enamel surface, while its cleavage products concentrate in the rod and interrod enamel. Processed enamel proteins accumulate during the secretory stage, but disappear early in the maturation stage. Enamel matrix serine proteinase 1 (EMSP1), now officially designated kallikrein 4 (KLK4), is believed to be the predominant degradative enzyme that clears enamel proteins from the matrix during maturation. KLK4 expression initiates during the transition stage and continues throughout maturation. KLK4 concentrates at the enamel surface when the enamel matrix disappears, and aggressively degrades amelogenin in vitro. During tooth development, proteinases are secreted by ameloblasts into the extracellular space, where they cleave enamel proteins by catalyzing the hydrolysis of peptide bonds. Enamel proteinases are present in low abundance and are not likely to participate directly in the mineralization process. Two major enamel proteinases have been identified: enamelysin (MMP20) and kallikrein 4 (KLK4). These proteinases are expressed at different times and have different functions. Their roles are to modify and/or to eliminate enamel matrix proteins, which affects the way enamel proteins interact with each other and with the developing enamel crystallites. A brief review of dental enamel formation is presented, followed by a more detailed analysis of enamelysin and KLK4 expression, structure, and function.
它们（a）加工和（b）降解牙釉质蛋白。不同的酶执行这些功能。釉质溶解素（基质金属蛋白酶-20，MMP-20）是首要的牙釉质基质加工酶。其表达在牙本质矿化开始之前启动，并在釉质发生的分泌阶段持续存在。在体外，釉质溶解素催化所有已知在体内分泌阶段发生的釉原蛋白裂解，它可能是负责加工所有牙釉质蛋白的酶。有证据表明釉质溶解素活性对正常牙釉质形成至关重要。未裂解和已加工的牙釉质蛋白常常在发育中的牙釉质层内分隔到不同的区域，这表明它们可能具有不同的功能。完整的成釉蛋白及其C端裂解产物定位于表层釉柱和柱间质，而其N端裂解产物聚集在鞘间隙。完整的釉蛋白仅存在于距牙釉质表面1微米内的矿化前沿，而其裂解产物集中在釉柱和柱间质。已加工的牙釉质蛋白在分泌阶段积累，但在成熟阶段早期消失。牙釉质基质丝氨酸蛋白酶1（EMSP1），现正式命名为激肽释放酶4（KLK4），被认为是在成熟过程中从基质中清除牙釉质蛋白的主要降解酶。KLK4的表达在过渡阶段开始，并在整个成熟过程中持续。当牙釉质基质消失时，KLK4集中在牙釉质表面，并在体外积极降解釉原蛋白。在牙齿发育过程中，蛋白酶由成釉细胞分泌到细胞外空间，在那里它们通过催化肽键的水解来裂解牙釉质蛋白。牙釉质蛋白酶含量低，不太可能直接参与矿化过程。已鉴定出两种主要的牙釉质蛋白酶：釉质溶解素（MMP20）和激肽释放酶4（KLK4）。这些蛋白酶在不同时间表达，具有不同功能。它们的作用是修饰和/或消除牙釉质基质蛋白，这会影响牙釉质蛋白彼此之间以及与正在发育的牙釉质微晶之间的相互作用方式。本文首先简要回顾牙釉质形成过程，随后更详细地分析釉质溶解素和KLK4的表达、结构及功能。
