Biophysical characterization of the Plasmodium falciparum circumsporozoite protein's N-terminal domain.

The circumsporozoite protein (CSP) is the main surface antigen of the Plasmodium sporozoite (SPZ) and forms the basis of the currently only licensed anti-malarial vaccine (RTS,S/AS01). CSP uniformly coats the SPZ and plays a pivotal role in its immunobiology, in both the insect and the vertebrate hosts. Although CSP's N-terminal domain (CSP ) has been reported to play an important role in multiple CSP functions, a thorough biophysical and structural characterization of CSP is currently lacking. Here, we present an alternative method for the recombinant production and purification of CSP from Plasmodium falciparum (PfCSP ), which provides pure, high-quality protein preparations with high yields. Through an interdisciplinary approach combining in-solution experimental methods and in silico analyses, we provide strong evidence that PfCSP is an intrinsically disordered region displaying some degree of compaction.