Multiple Selected Changes May Modulate the Molecular Interaction between Laverania RH5 and Primate Basigin

Recently, Plenderleith et al. generated sequences of Laverania RH5 genes and analyzed their evolutionary history (1). Much of their efforts focus on criticism of a study in which we analyzed the evolution of RH5 (with much fewer sequences) and of primate basigin (BSG), the ligand for RH5 (2). Plenderleith et al. mistakenly quote sentences from our work and erroneously criticize our analyses (e.g., branch lengths were not “distorted,” they were simply not reported). Notably, when Plenderleith et al. (1) mention our results on BSG, they fail to mention that, in addition to searching for evidence of selection in an extended primate phylogeny, we applied a phylogenetics-population genetics method (3) to search for sites that were positively selected in the human, chimpanzee, and gorilla lineages. Three of the sites we detected (Fig. 1) are located at the interaction surface with Plasmodium falciparum RH5 (PfRH5), and two of them strongly affect PfRH5 binding (4). When introduced into human BSG, the F27L change, which occurred in the gorilla lineage, causes an eightfold reduction in binding. As for residue 191, when the human amino acid (K) is introduced into the chimpanzee BSG protein (191E), the latter binds PfRH5 with much higher affinity (4). A conceivable interpretation of these findings is that chimpanzee and gorilla BSG evolved to avoid RH5 binding and, therefore, that positive selection at BSG contributed to determine species-specific interactions. Concerning the analysis of RH5, we acknowledged in our work that we had little power to detect selection (see Discussion [2]), and we agree that we had no possibility to determine when selection acted. However, branch-site tests are robust to the inclusion of distantly related sequences and paralogs (5, 6). In fact, we identified two selected sites, one of which (position 447) was also detected by Plenderleith et al., who used BUSTED to search for selection across an RH5 Laverania phylogeny. We have now applied two branch-site tests, the “MA/MA1” test and BUSTED to a phylogeny of almost complete RH5 sequences (Fig. 1). These methods allow the rigorous testing of a priori-specified branches for evidence of episodic positive selection. We used three methods to identify selected sites on branches showing evidence of selection (Fig. 1 and Table 1). Our results indicate the following. (i) The strongest selection occurred on the long branches that separate Plasmodium reichenowi/Plasmodium billcollinsi from the other Laverania. (ii) Selected sites include the two we had previously detected (190 and 447) and most of those described by Plenderleith et al. (1). (iii) No evidence of selection was detected on the P. falciparum branch. (iv) Selection at the 197 site, discussed by Plenderleith et al., most likely occurred in the ancestor of Plasmodium adleri and P. falciparum/Plasmodium praefalciparum. This clearly does not rule out the possibility that 197S in PfRH5 modulates binding. Published 22 May 2018 Citation Forni D, Pontremoli C, Cagliani R, Pozzoli U, Clerici M, Sironi M. 2018. Multiple selected changes may modulate the molecular interaction between Laverania RH5 and primate basigin. mBio 9:e00476-18. https://doi . org/10.1128/mBio.00476-18. Invited Editor Harmit S. Malik, Fred Hutchinson Cancer Research Center Editor Stephen P. Goff, Columbia University Copyright © 2018 Forni et al. This is an openaccess article distributed under the terms of the Creative Commons Attribution 4.0 International license. Address correspondence to Diego Forni, diego.forni@bp.lnf. it. For the author reply, see https://doi.org/10 . 1128/mBio.00917-18. LETTER TO THE EDITOR