Beta-thymosins from marine invertebrates: primary structure and interaction with actin

Area of Science:

• Biochemistry
• Molecular Biology
• Evolutionary Biology

Background:

• Beta-thymosins are conserved actin-binding proteins found across vertebrate species.
• Their presence and function in invertebrates remain largely unexplored.
• Actin dynamics are crucial for cellular processes in all eukaryotes.

Purpose of the Study:

• To investigate the existence and function of beta-thymosin-like peptides in invertebrates.
• To characterize novel actin-binding proteins from sea urchins and scallops.
• To compare invertebrate beta-thymosins with their vertebrate homologs.

Main Methods:

• Fractionation of perchloric acid extracts from sea urchin and scallop gonads.
• Crosslinking assays to identify actin-binding peptides.
• Peptide sequencing to determine amino acid composition and identity.
• In vitro assays to assess inhibition of actin polymerization and nucleotide exchange.

Main Results:

• Identified and sequenced 40-amino acid beta-thymosin-like peptides from both sea urchin (Arbacia punctulata) and scallop (Argopecten irradians).
• These invertebrate peptides share significant sequence identity (72-80%) with vertebrate beta-thymosins.
• The sea urchin peptide inhibited actin polymerization and nucleotide exchange, albeit with lower affinity than thymosin beta4.

Conclusions:

• Beta-thymosin-like proteins are present and functional in invertebrates, binding actin monomers.
• These findings suggest an ancient evolutionary origin for beta-thymosin's role in actin regulation.
• Invertebrate beta-thymosins offer valuable models for studying actin dynamics and evolution.