Tanaka T, Miwa N, Kawamura S, Sohma H, Nitta K, Matsushima N
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Kita-ku, Sapporo, Hokkaido 060-0810, Japan.
Protein Eng. 1999 May;12(5):395-405. doi: 10.1093/protein/12.5.395.
P26olf from olfactory tissue of frog, which may be involved in olfactory transduction or adaptation, is a Ca2+-binding protein with 217 amino acids. The p26olf molecule contains two homologous parts consisting of the N-terminal half with amino acids 1-109 and the C-terminal half with amino acids 110-217. Each half resembles S100 protein with about 100 amino acids and contains two helix-loop-helix Ca2+-binding structural motifs known as EF-hands: a normal EF-hand at the C-terminus and a pseudo EF-hand at the N-terminus. Multiple alignment of the two S100-like domains of p26olf with 18 S100 proteins indicated that the C-terminal putative EF-hand of each domain contains a four-residue insertion when compared with the typical EF-hand motifs in the S100 protein, while the N-terminal EF-hand is homologous to its pseudo EF-hand. We constructed a three-dimensional model of the p26olf molecule based on results of the multiple alignment and NMR structures of dimeric S100B(betabeta) in the Ca2+-free state. The predicted structure of the p26olf single polypeptide chain satisfactorily adopts a folding pattern remarkably similar to dimeric S100B(betabeta). Each domain of p26olf consists of a unicornate-type four-helix bundle and they interact with each other in an antiparallel manner forming an X-type four-helix bundle between the two domains. The two S100-like domains of p26olf are linked by a loop with no steric hindrance, suggesting that this loop might play an important role in the function of p26olf. The circular dichroism spectral data support the predicted structure of p26olf and indicate that Ca2+-dependent conformational changes occur. Since the C-terminal putative EF-hand of each domain fully keeps the helix-loop-helix motif having a longer Ca2+-binding loop, regardless of the four-residue insertion, we propose that it is a new, novel EF-hand, although it is unclear whether this EF-hand binds Ca2+. P26olf is a new member of the S100 protein family.
来自青蛙嗅觉组织的P26olf是一种含217个氨基酸的钙结合蛋白，可能参与嗅觉转导或适应过程。p26olf分子包含两个同源部分，由含1 - 109个氨基酸的N端半部分和含110 - 217个氨基酸的C端半部分组成。每一半都类似于含约100个氨基酸的S100蛋白，并包含两个称为EF手型的螺旋-环-螺旋钙结合结构基序：C端的正常EF手型和N端的假EF手型。p26olf的两个类S100结构域与18种S100蛋白的多重比对表明，与S100蛋白中的典型EF手型基序相比，每个结构域的C端假定EF手型含有一个四残基插入，而N端EF手型与其假EF手型同源。我们基于多重比对结果和无钙状态下二聚体S100B（ββ）的核磁共振结构构建了p26olf分子的三维模型。预测的p26olf单条多肽链结构令人满意地采用了与二聚体S100B（ββ）非常相似的折叠模式。p26olf的每个结构域由单角型四螺旋束组成，它们以反平行方式相互作用，在两个结构域之间形成X型四螺旋束。p26olf的两个类S100结构域由一个无空间位阻的环连接，表明该环可能在p26olf的功能中起重要作用。圆二色光谱数据支持p26olf的预测结构，并表明发生了钙依赖性构象变化。由于每个结构域的C端假定EF手型完全保留了具有较长钙结合环的螺旋-环-螺旋基序，尽管有四残基插入，我们提出它是一种新的、新颖的EF手型，尽管尚不清楚该EF手型是否结合钙。P26olf是S100蛋白家族的新成员。
