Use of staphylococcal protein A in the analysis of teleost immunoglobulin structural diversity

Staphylcoccal protein A (SpA) adsorption and sephacryl-S300 filtration were employed to isolate Ig from the sera of six aquaculturally important teleost species; Morone saxatilis (striped bass), Lates calcarifer (barramundi), Oreochromis mossambicus (Mozambique tilapia) and Oreochromis niloticus (Nile tilapia), Salmo salar (Atlantic salmon), and Oncorhynchus mykiss (rainbow trout). While both gel filtration (S300) and SpA adsorption could purify the 800 kDa tetrameric Ig, SpA demonstrated species-specific variability in the amount retrieved. Virtually 100% of this high molecular weight Ig could be isolated from Mosambique tilapia serum, while 84, 17, 10.7 and 0.5% could be isolated from barramundi, striped bass, Nile tilapia, and Atlantic salmon, respectively. Significant amounts of Ig could not be isolated (<0.1%) from rainbow trout (O. mykiss) serum. All SpA-isolated proteins were approximately 800 kDa in molecular weight and were solely composed of equimolar concentrations of H ( approximately 75 kDa) and L ( approximately 25 kDa) chains. Denaturing, non-reducing electrophoresis demonstrated differential disulfide polymerization (redox forms) consistent with those observed with other teleost species; however, SpA exhibited less affinity for Ig possessing completely polymerized tetramers than the more reduced forms, with the exception of Mossambique tilapia. The existence of three different molecular weight H chains (75, 85, 95 kDa) in Nile tilapia was also observed. Each redox form of Nile tilapia Ig incorporated only one size of H chain.