Wustman Brandon A, Morse Daniel E, Evans John Spencer
Laboratory for Chemical Physics, New York University, 345 E. 24th Street, New York, NY 10010, USA.
Biopolymers. 2004 Aug 5;74(5):363-76. doi: 10.1002/bip.20086.
The AP7 and AP24 proteins represent a class of mineral-interaction polypeptides that are found in the aragonite-containing nacre layer of mollusk shell (H. rufescens). These proteins have been shown to preferentially interfere with calcium carbonate mineral growth in vitro. It is believed that both proteins play an important role in aragonite polymorph selection in the mollusk shell. Previously, we demonstrated the 1-30 amino acid (AA) N-terminal sequences of AP7 and AP24 represent mineral interaction/modification domains in both proteins, as evidenced by their ability to frustrate calcium carbonate crystal growth at step edge regions. In this present report, using free N-terminal, C(alpha)-amide "capped" synthetic polypeptides representing the 1-30 AA regions of AP7 (AP7-1 polypeptide) and AP24 (AP24-1 polypeptide) and NMR spectroscopy, we confirm that both N-terminal sequences possess putative Ca (II) interaction polyanionic sequence regions (2 x -DD- in AP7-1, -DDDED- in AP24-1) that are random coil-like in structure. However, with regard to the remaining sequences regions, each polypeptide features unique structural differences. AP7-1 possesses an extended beta-strand or polyproline type II-like structure within the A11-M10, S12-V13, and S28-I27 sequence regions, with the remaining sequence regions adopting a random-coil-like structure, a trait common to other polyelectrolyte mineral-associated polypeptide sequences. Conversely, AP24-1 possesses random coil-like structure within A1-S9 and Q14-N16 sequence regions, and evidence for turn-like, bend, or loop conformation within the G10-N13, Q17-N24, and M29-F30 sequence regions, similar to the structures identified within the putative elastomeric proteins Lustrin A and sea urchin spicule matrix proteins. The similarities and differences in AP7 and AP24 N-terminal domain structure are discussed with regard to joint AP7-AP24 protein modification of calcium carbonate growth.
AP7和AP24蛋白代表一类矿物质相互作用多肽，存在于软体动物贝壳（红鲍）含文石的珍珠层中。这些蛋白已被证明在体外能优先干扰碳酸钙矿物的生长。据信这两种蛋白在软体动物贝壳的文石多晶型选择中都起着重要作用。此前，我们证明了AP7和AP24的1 - 30个氨基酸（AA）的N端序列代表了这两种蛋白中的矿物质相互作用/修饰结构域，这一点可由它们在台阶边缘区域抑制碳酸钙晶体生长的能力得到证明。在本报告中，我们使用代表AP7（AP7 - 1多肽）和AP24（AP24 - 1多肽）的1 - 30 AA区域的游离N端、C（α） - 酰胺“封端”合成多肽以及核磁共振光谱，证实这两个N端序列都具有假定的Ca（II）相互作用聚阴离子序列区域（AP7 - 1中有2个 - DD - ，AP24 - 1中有 - DDDED - ），其结构呈无规卷曲状。然而，关于其余序列区域，每个多肽都有独特的结构差异。AP7 - 1在A11 - M10、S12 - V13和S28 - I27序列区域具有延伸的β - 链或多聚脯氨酸II型样结构，其余序列区域呈无规卷曲状结构，这是其他聚电解质矿物质相关多肽序列共有的特征。相反，AP24 - 1在A1 - S9和Q14 - N16序列区域具有无规卷曲状结构，在G10 - N13、Q17 - N24和M29 - F30序列区域有类似转角、弯曲或环的构象证据，类似于在假定的弹性蛋白Lustrin A和海胆刺基质蛋白中鉴定出的结构。我们讨论了AP7和AP24 N端结构域结构的异同，涉及到AP7 - AP24联合蛋白对碳酸钙生长的修饰作用。
