Conservation and plasticity in avian prepro-GnRH-I reflect a modular evolutionary architecture

Abstract

Gonadotropin-releasing hormone type I (GnRH-I) is produced from the GNRH1-encoded prepro-GnRH-I precursor, which comprises a signal peptide (SP), the GnRH-I decapeptide, the Gly-Lys-Arg (GKR) processing motif, and the GnRH-associated peptide (GAP). Here, we evaluated conservation and plasticity across avian prepro-GnRH-I using 61 mRNA sequences representing 32 avian orders through multiple alignment, site-specific conservation, locus-based phylogenetic inference, hydropathy profiling, secondary- and tertiary-structure prediction, and phosphorylation-site prediction. Comparisons were performed against a study-specific avian consensus sequence generated from the analyzed alignment. The GnRH-I decapeptide and GKR motif were highly conserved, whereas sequence variability was concentrated mainly in SP and GAP. Nucleotide identity relative to the consensus varied among orders, with higher similarity in Accipitriformes and Cariamiformes, lower similarity in Passeriformes, and intermediate values in Anseriformes and Galliformes. Rare predicted amino acid substitutions were detected within the decapeptide. Hydropathy analysis supported a modular secretory architecture, with a hydrophobic SP and predominantly hydrophilic GnRH-I, GKR, and GAP regions. Secondary-structure prediction indicated substantial α-helical content in SP and GAP, whereas GnRH-I was predicted to adopt a predominantly coil-like/flexible conformation. Homology modeling positioned GAP within a helix–loop–helix-like organization, and predicted phosphorylation sites were concentrated mainly in GAP. These computational findings support a modular evolutionary framework for avian prepro-GnRH-I and identify GAP as a structurally coherent, evolutionarily plastic candidate module requiring experimental validation.