Chan David I, Hunter Howard N, Tack Brian F, Vogel Hans J
Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.
Antimicrob Agents Chemother. 2008 Mar;52(3):883-94. doi: 10.1128/AAC.00805-07. Epub 2007 Dec 17.
Human macrophage inflammatory protein 3alpha (MIP-3alpha), also known as CCL20, is a 70-amino-acid chemokine which exclusively binds to chemokine receptor 6. In addition, the protein also has direct antimicrobial, antifungal, and antiviral activities. The solution structure of MIP-3alpha was solved by the use of two-dimensional homonuclear proton nuclear magnetic resonance (NMR). The structure reveals the characteristic chemokine fold, with three antiparallel beta strands followed by a C-terminal alpha helix. In contrast to the crystal structures of MIP-3alpha, the solution structure was found to be monomeric. Another difference between the NMR and crystal structures lies in the angle of the alpha helix with respect to the beta strands, which measure 69 and approximately 56.5 degrees in the two structures, respectively. NMR diffusion and pH titration studies revealed a distinct tendency for MIP-3alpha to form dimers at neutral pH and monomers at lower pH, dependent on the protonation state of His40. Molecular dynamics simulations of both the monomeric and the dimeric forms of MIP-3alpha supported the notion that the chemokine undergoes a change in helix angle upon dimerization and also highlighted the important hydrophobic and hydrogen bonding contacts made by His40 in the dimer interface. Moreover, a constrained N terminus and a smaller binding groove were observed in dimeric MIP-3alpha simulations, which could explain why monomeric MIP-3alpha may be more adept at receptor binding and activation. The solution structure of a synthetic peptide consisting of the last 20 residues of MIP-3alpha displayed a highly amphipathic alpha helix, reminiscent of various antimicrobial peptides. Antimicrobial assays with this peptide revealed strong and moderate bactericidal activities against Escherichia coli and Staphylococcus aureus, respectively. This confirms that the C-terminal alpha-helical region of MIP-3alpha plays a significant part in its broad anti-infective activity.
人巨噬细胞炎性蛋白3α（MIP-3α），也称为CCL20，是一种由70个氨基酸组成的趋化因子，它只与趋化因子受体6结合。此外，该蛋白还具有直接的抗菌、抗真菌和抗病毒活性。MIP-3α的溶液结构是通过二维同核质子核磁共振（NMR）解析得到的。该结构揭示了趋化因子的特征性折叠，即三条反平行的β链后接一个C端α螺旋。与MIP-3α的晶体结构不同，溶液结构被发现是单体形式。NMR结构和晶体结构的另一个差异在于α螺旋相对于β链的角度，在这两种结构中分别为69度和大约56.5度。NMR扩散和pH滴定研究表明，MIP-3α在中性pH下有形成二聚体的明显趋势，而在较低pH下为单体，这取决于His40的质子化状态。MIP-3α单体和二聚体形式的分子动力学模拟支持了趋化因子在二聚化时螺旋角度发生变化的观点，同时也突出了His40在二聚体界面形成的重要疏水和氢键接触。此外，在二聚体MIP-3α模拟中观察到一个受限的N端和一个较小的结合凹槽，这可以解释为什么单体MIP-3α可能更擅长受体结合和激活。由MIP-3α最后20个残基组成的合成肽的溶液结构显示出高度两亲性的α螺旋，让人联想到各种抗菌肽。用该肽进行的抗菌试验分别显示出对大肠杆菌和金黄色葡萄球菌的强杀菌活性和中等杀菌活性。这证实了MIP-3α的C端α螺旋区域在其广泛的抗感染活性中起重要作用。
