Toward the elucidation of the mechanism of attachment and entry of malaria sporozoites into cells: synthetic polypeptides from the circumsporozoite protein of Plasmodium falciparum bind Ca2+ and interact with model phospholipid membranes.

Through the joint use of CD, Fourier transform ir (FTIR), and attenuated total reflectance FTIR we have found that synthetic polypeptide models of the Plasmodium falciparum circumsporozoite (CS) protein repeat domain bind calcium ions in helicogenic environments. Ca(2+)-(NANP)n complexes (n greater than or equal to 20) interact vectorially with model phospholipid membranes orienting their polypeptide axes preferentially along those of the lipid acyl chains. It is proposed that the P. falciparum CS protein central region, rather than acting as a molecular lure helping the parasite to evade host immune control, plays, as a specific Ca2+ macroligand, a critical functional role during attachment, invasion, and development of the malaria parasite in the hepatic cell.

EPR characterization of cellulose triacetate fibers used for enzyme immobilization.

EPR studies of a nitroxide spin label and of the nitroxide spin-labeled albumin entrapped in cellulose triacetate fibers were carried out.The EPR spectra have shown that within the fiber only two phases are present: a liquid one of medium viscosity trapped inside microcavities, and a polymeric one surrounding them.After entrapment, spin-labeled albumin is distributed mainly in the liquid phase, though a not negligible amount of it remains within the polymeric matrix.The EPR studies have shown that, after the standard procedure of drying, the albumin is almost completely precipitated, but about 85% of it returns to solution when the fiber is again placed in the solution.The behavior of the albumin dissolved inside the microcavities toward denaturating agents and pH change, and that of the free albumin in solution is similar; the minor differences noticed indicate a second-order interaction between the fiber and the protein.