A Possible Molecular Ancestor for Mollusk APGWamide, Insect Adipokinetic Hormone, and Crustacean Red Pigment Concentrating Hormone

May 25, 2002Journal of molecular evolution

A possible shared molecular ancestor of mollusk APGWamide, insect energy hormone, and crustacean color hormone

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Abstract

DNA sequence alignments indicate that the APGWamide genes are larger than the AKH/RPCH genes.

Comparative analysis of neuropeptide precursor structures shows a similar overall design across the AKH/RPCH and APGWamide families.
Amino acid sequences reveal a common secondary structure, characterized by an alpha helix and random coil arrangement.
Gene similarities suggest that AKH/RPCH and APGWamide families may have evolved from a shared ancestor through gene rearrangements.
The intron sequence environments in both gene families exhibit notable similarities.
Evidence points to different evolutionary paths for the two families, with the APGWamide precursors showing closer resemblance to the RPCH family than to the AKH family.

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Precursor structures of various members of the neuropeptide family adipokinetic hormone/red pigment concentrating hormone (AKH/RPCH) of mandibular arthropods and the APGWamide family of mollusks were compared. Amino acid alignments showed a common overall architecture (signal peptide, active peptide, related peptide), with a similar alpha helix-random coil secondary structure. DNA sequence alignments revealed close similarities between the genes encoding for the peptides of the two families. The APGWamide genes are larger than the AKH/RPCH genes. The sequence environment occupied by introns is similar in AKH/RPCH and APGWamide genes. Such similarities suggest that these peptide families might have been originated by gene rearrangements from a common ancestor having either an AKH/RPCH/APGWamide-like structure or both an AKH/RPCH-like and an APGWamide-like structures. In the former model, DNA fragments could have been gained when the ancestor evolved to mollusks and it could have lost nucleotides when the progression to mandibular arthropods took place. In the second model, AKH/RPCH-like structures could have been fused during evolution toward mandibular arthropods, whereas in mollusks they could have been lost with the possible amplification of the APGWamide-like structure. Loss of domains in exon 1 may have originated the signal peptide and the first codon of the active RPCH. In exon 2, loss of domains possibly determined the junctions of codons 2 to 5 with the loss of a APGWamide copy; exon 3 underwent fewer variations. The similarity of the mollusk APGWamide precursors is closer to that of the RPCH family than the insect AKH family, indicating an earlier evolutionary departure.

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A Possible Molecular Ancestor for Mollusk APGWamide, Insect Adipokinetic Hormone, and Crustacean Red Pigment Concentrating Hormone

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