Hatherley Rowan, Blatch Gregory L, Bishop Ozlem Tastan
a Department of Biochemistry, Microbiology and Biotechnology, Rhodes University Bioinformatics (RUBi) , Rhodes University , Grahamstown , 6140 , South Africa .
J Biomol Struct Dyn. 2014;32(11):1766-79. doi: 10.1080/07391102.2013.834849. Epub 2013 Sep 13.
Plasmodium falciparum 70 kDa heat shock proteins (PfHsp70s) are expressed at all stages of the pathogenic erythrocytic phase of the malaria parasite life cycle. There are six PfHsp70s, all of which have orthologues in other plasmodial species, except for PfHsp70-x which is unique to P. falciparum. This research highlights a number of original results obtained by a detailed bioinformatics analysis of the protein. Large-scale sequence analysis indicated the presence of an extended transit peptide sequence of PfHsp70-x which potentially directs it to the endoplasmic reticulum (ER). Further analysis showed that PfHsp70-x does not have an ER-retention sequence, suggesting that the protein transits through the ER and is secreted into the parasitophorous vacuole or beyond into the erythrocyte cytosol. These results are consistent with experimental findings. Next, possible interactions between PfHsp70-x and exported P. falciparum Hsp40s or host erythrocyte Hsp40 were interrogated by modelling and docking. Docking results indicated that interaction between PfHsp70-x and each of the Hsp40s, regardless of biological feasibility, seems equally likely. This suggests that J domain might not provide the specificity in the formation of unique Hsp70-Hsp40 complexes, but that the specificity might be provided by other domains of Hsp40s. By studying different structural conformations of PfHsp70-x, it was shown that Hsp40s can only bind when PfHsp70-x is in a certain conformation. Additionally, this work highlighted the possible dependence of the substrate-binding domain residues on the orientation of the α-helical lid for formation of the substrate-binding pocket.
恶性疟原虫70 kDa热休克蛋白（PfHsp70s）在疟原虫生命周期的致病性红细胞阶段的所有时期均有表达。有六种PfHsp70s，除PfHsp70-x是恶性疟原虫所特有的外，其余在其他疟原虫物种中均有直系同源物。本研究突出了通过对该蛋白进行详细的生物信息学分析所获得的一些原创性结果。大规模序列分析表明PfHsp70-x存在一个延伸的转运肽序列，该序列可能将其导向内质网（ER）。进一步分析表明PfHsp70-x没有内质网滞留序列，这表明该蛋白穿过内质网并分泌到寄生泡或进入红细胞胞质溶胶。这些结果与实验发现一致。接下来，通过建模和对接研究了PfHsp70-x与输出的恶性疟原虫Hsp40s或宿主红细胞Hsp40之间可能的相互作用。对接结果表明，无论生物学可行性如何，PfHsp70-x与每种Hsp40之间的相互作用似乎同样可能。这表明J结构域可能在形成独特的Hsp70-Hsp40复合物时不提供特异性，而特异性可能由Hsp40s的其他结构域提供。通过研究PfHsp70-x的不同结构构象，结果表明只有当PfHsp70-x处于特定构象时Hsp40s才能结合。此外，这项工作突出了底物结合结构域残基可能依赖于α-螺旋盖的方向来形成底物结合口袋。
