Duplicate Abalone Egg Coat Proteins Bind Sperm Lysin Similarly, but Evolve Oppositely, Consistent with Molecular Mimicry at Fertilization
Figure 3
Positively selected residues occupy the exposed surface of egg coat proteins.
Positively selected sites of the (A) VERL and (B) VEZP14 ZP-N motifs were inferred among 8 North Pacific abalone taxa using the Bayes Empirical Bayes (BEB) procedure of codeml [49], and sites with high posterior probabilities (>95%) were mapped to the respective structural models [22] using PyMol [52]. The positions of positively selected sites are given with reference to the complete coding sequences of VEZP14 and VERL (repeat 1 only) from red abalone ([19] and [15], respectively). For VERL, the single site under positive selection identified with high posterior probability (V42) was inferred from the first two full VERL repeats, as statistical power from concatenated ZP-N motifs alone is insufficient to allow for predicting sites under selection via BEB (Table 1). This site occupies the same position of the structural model for ZP-N from VEZP14 (S171), with the majority of the remaining seven residues predicted to be under positive selection (N173, R187, E209, I218, L220, K228, and A233) occuring on the same exposed surface opposite the E′ extension (grey fill) thought to facilitate antiparallel pairing among intermolecular ZP-N motifs [23].