THE SECONDARY STRUCTURE AND AGGREGATION OF LYOPHILIZED TETANUS TOXOID

Tetanus toroid (TT), the vaccine for tetanus, is an important protein antigen and candidate for sustained release from polymeric matrices. D uring administration from the latter, the solid (e.g., lyophilized) pr otein will be exposed to elevated levels of temperature and moisture, conditions which trigger its aggregation. To examine the connection be tween this aggregation and the structure of the TT molecule in the sol id state, Fourier-transform infrared (FTIR) spectroscopy was employed to determine the secondary structure of TT in the presence of various excipients. We found that excipient-free TT undergoes a significant al teration (mostly reversible) in the secondary structure during lyophil ization. Specifically, more than half the total alpha-helix content wa s lost with a concomitant increase in beta-sheet structure. The extent of structural alterations in the presence of 1:5 (g:g protein) NaCl, sorbitol, or poly(ethylene glycol), did not correlate with stability c onferred towards moisture-induced aggregation. These results suggest t hat the degree of retention of the native protein structure in the dry state is not a general predictor of stability for the ''wetted'' soli d within polymer controlled-release vehicles.