Geriatric Research, Education, and Clinical Center (11-E), VA Medical Center, VA Greater Los Angeles Health Care System, 16111 Plummer Street, Sepulveda, California 91343, USA.
J Orthop Res. 2010 Sep;28(9):1200-7. doi: 10.1002/jor.21102.
Secreted phosphoprotein-24 kDa (spp24) is a bone morphogenetic protein (BMP)-binding protein isolated from bone. It exists in a number of size forms and is hypothesized to function as a BMP latency protein and/or a "slow release" mechanism for BMPs involved in bone turnover and repair. We have examined the hypothesis that proteolytic modification of the C-terminus of spp24 affects its BMP-2-binding properties and bioactivity in the BMP-2-stimulated ectopic bone forming bioassay. Three different size forms of recombinant spp24 that correspond to predicted 18.1 kDa, 16.0 kDa, and 14.5 kDa proteolytic products were compared to full-length (fl) spp24. One of these forms (spp18.1) we hypothesize to be the protein which Urist initially, but apparently inaccurately, called "BMP." Only full-length spp24 completely inhibited BMP-2-induced bone formation. The 18.1 kDa truncated isoform of spp24 which we hypothesize to be Urist's protein did not. The inhibitory capacity of the proteins was correlated with their kinetic constants, assessed by surface plasmon resonance. At the highest, inhibitory, dose of spp24 and its derivatives, k(d) ("stability") best predicted the extent of ectopic bone formation whereas at the lowest dose, which was not inhibitory, k(a) ("recognition") best predicted the extent of ectopic bone formation. We conclude that proteolytic processing of spp24 affects the interaction of this protein with BMP-2 and this affects the function of the protein.
分泌型磷蛋白-24kDa（spp24）是一种从骨骼中分离出来的骨形态发生蛋白（BMP）结合蛋白。它存在于多种大小形式中，被假设为 BMP 潜伏蛋白和/或 BMP 参与骨转换和修复的“缓慢释放”机制。我们已经检验了这样一个假设，即 spp24 的 C 末端的蛋白水解修饰会影响其与 BMP-2 的结合特性和在 BMP-2 刺激的异位骨形成生物测定中的生物活性。三种不同大小形式的重组 spp24，分别对应于预测的 18.1kDa、16.0kDa 和 14.5kDa 蛋白水解产物，与全长（fl）spp24 进行了比较。我们假设其中一种形式（spp18.1）是 Urist 最初但显然不准确地称为“BMP”的蛋白。只有全长 spp24 完全抑制 BMP-2 诱导的骨形成。我们假设是 Urist 蛋白的 18.1kDa 截断同工型的 spp24 则没有。通过表面等离子体共振评估，蛋白质的抑制能力与它们的动力学常数相关。在 spp24 及其衍生物的最高抑制剂量下，k(d)（“稳定性”）最好地预测了异位骨形成的程度，而在最低剂量下，k(a)（“识别”）最好地预测了异位骨形成的程度。我们得出结论，spp24 的蛋白水解加工影响了该蛋白与 BMP-2 的相互作用，从而影响了该蛋白的功能。
