title: Force Spectroscopy of thePlasmodium falciparumVaccine Candidate Circumsporozoite Protein Suggests a Mechanically Pliable Repeat Region.
abstract: The most effective vaccine candidate of malaria is based on thePlasmodium falciparumcircumsporozoite protein (CSP), a major surface protein implicated in the structural strength, motility, and immune evasion properties of the infective sporozoites. It is suspected that reversible conformational changes of CSP are required for infection of the mammalian host, but the detailed structure and dynamic properties of CSP remain incompletely understood, limiting our understanding of its function in the infection. Here, we report the structural and mechanical properties of the CSP studied using single-molecule force spectroscopy on several constructs, one including the central region of CSP, which is rich in NANP amino acid repeats (CSPrep), and a second consisting of a near full-length sequence without the signal and anchor hydrophobic domains (CSPΔHP). Our results show that the CSPrepis heterogeneous, with 40% of molecules requiring virtually no mechanical force to unfold (<10 piconewtons (pN)), suggesting that these molecules are mechanically compliant and perhaps act as entropic springs, whereas the remaining 60% are partially structured with low mechanical resistance (∼70 pN). CSPΔHPhaving multiple force peaks suggests specifically folded domains, with two major populations possibly indicating the open and collapsed forms. Our findings suggest that the overall low mechanical resistance of the repeat region, exposed on the outer surface of the sporozoites, combined with the flexible full-length conformations of CSP, may provide the sporozoites not only with immune evasion properties, but also with lubricating capacity required during its navigation through the mosquito and vertebrate host tissues. We anticipate that these findings would further assist in the design and development of future malarial vaccines.
authors.affiliation: From the Departments of Biological Sciences and.
authors.forename: Aditya Prasad
authors.initials: AP
authors.lastname: Patra
authors.affiliation: From the Departments of Biological Sciences and sharma@tifr.res.in.
authors.forename: Shobhona
authors.initials: S
authors.lastname: Sharma
authors.affiliation: Chemical Sciences, Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai 400005, India koti@tifr.res.in.
authors.forename: Sri Rama Koti
authors.identifier: 0000-0002-1646-2731
authors.initials: SR
authors.lastname: Ainavarapu
mesh_terms: D000818:Animals; D057927:Hydrophobic and Hydrophilic Interactions; D017780:Malaria Vaccines / Q000737:chemistry* / Q000276:immunology; D010963:Plasmodium falciparum / Q000276:immunology*; D011487:Protein Conformation; D058767:Protein Unfolding; D015800:Protozoan Proteins / Q000737:chemistry* / Q000276:immunology; D013057:Spectrum Analysis / Q000379:methods*
chemical_list: D017780:Malaria Vaccines; D015800:Protozoan Proteins; C041595:circumsporozoite protein, Protozoan
keywords: NANP; NANP repeats; Plasmodium falciparum; atomic force microscopy (AFM); circumsporozoite protein (CSP); force spectroscopy; malaria; malaria parasite; plasmodium; proline-rich peptides; proline-rich protein; single-molecule biophysics; sporozoite; structural biology