Three ryanodine receptor isoforms exist in avian striated muscles

Area of Science:

• Biochemistry
• Molecular Biology
• Muscle Physiology

Background:

• Avian fast twitch skeletal muscle coexpresses two ryanodine receptor (RyR) isoforms (alpha and beta).
• Avian cardiac muscle expresses a single RyR isoform.
• The relationship between these three RyR proteins in chicken striated muscles is not fully understood.

Purpose of the Study:

• To investigate the relationship between the three chicken ryanodine receptor isoforms.
• To compare the biochemical and immunological properties of avian skeletal and cardiac RyR isoforms.

Main Methods:

• Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for protein mobility.
• Monoclonal antibody epitope mapping.
• Limited tryptic digestion and peptide mapping.
• Phosphorylation assays using calcium/calmodulin-dependent protein kinase II.
• Calmodulin binding assays using azido[125I]calmodulin.

Main Results:

• The three RyR isoforms exhibit distinct mobilities on SDS-PAGE.
• Monoclonal antibodies reveal unique and shared epitopes among the isoforms.
• Isoforms show differential susceptibility to trypsin digestion, yielding unique peptide maps.
• Phosphorylation levels by Ca2+/calmodulin-dependent protein kinase II vary (beta > cardiac > alpha).
• Phosphorylation sites differ between cardiac and skeletal isoforms.
• Calmodulin binding affinity varies: alpha > beta > cardiac.

Conclusions:

• Three distinct ryanodine receptor proteins are expressed in chicken striated muscles.
• These isoforms possess unique biochemical and immunological properties.
• The observed differences suggest specialized functions for each RyR isoform in avian muscle types.