An Interplay between KMP-11 Induced Phase Alteration of Macrophage Membrane and Immune Suppression Defines the Molecular Mechanism of Leishmaniasis

Abstract

Protein induced phase transition in the cellular membrane plays a vital role in many cellular processes including endocytosis and signal transduction. Change of temperature, lipid composition and inclusion of biological molecules could result in the alteration of the physical state of the membranes.The membrane fluidity and physical state have direct implications in the internalization of infecting parasites inside host macrophages. These parameters also determine the ability of microorganisms to adapt to changing environments through successful immune suppression. In this study, we show that a small immunogenic protein, KMP-11, derived from Leishmania donovani, induces phase transition in phospholipid membrane. The interaction of KMP-11 into the macrophage mimicking membrane leads to gel to fluid transition, which in turn facilitates the infection leading to the uptake of the parasite into macrophages. It is evident from small angle x-ray scattering (SAXS) that KMP-11 induces the phase transition at a threshold protein concentration, which is linked to the change in membrane tension. Subsequently, we have used tryptophan-scanning mutagenesis to obtain insights into the role of hydrophobicity on the interaction of the protein with phospholipid membranes. Using the help of DPH anisotropy, Laurdan polarization, MHC class II expression by FACS measurement,IL2 expression and confocal imaging of the lipid rafts of macrophage under parasitized condition and KMP-11 treatment, we have shown that KMP-11 induced phase state alteration in macrophage membrane has direct consequence with the survival of parasite inside host cell through efficient immune suppression.