The Structure of Fibril-Forming SEM1(86-107) Peptide Increasing the HIV Infectivity

Abstract

SEM1(86-107) peptide is a cleavage product of semenogelin 1 (SEM1) expressed in seminal vesicles. SEM1(86-107) forms amyloid fibrils in semen increasing HIV infectivity by up to 3–5 orders of magnitude. The study of fibrillation process includes peptide spatial structure determination. This paper presents the information about the SEM1(86-107) structure obtained by the Nuclear Magnetic Resonance (NMR) spectroscopy and Circular Dichroism (CD) spectroscopy. Assignment of hydrogen chemical shifts and internuclear distances of the SEM1(86-107) with following prediction of secondary structure was carried out by the NMR spectroscopy. Also the spatial structure was calculated using the XPLOR-NIH software. The spatial structure analysis has shown the containing the regions with the random coil conformations in the SEM1(86-107) peptide. Analysis of the structure ensemble showed containing fragments with high convergence: Leu87-Lys92, Thr94-Gln97, and Gln104-Leu107. It can be assumed that these fragments are responsible for the fibrillation process via low their mobility. CD spectroscopy was applied to determine the secondary structure of SEM1(86-107). CD measurement confirmed that the prevailing secondary structure content of SEM1(86-107) peptide is a random coil.