Le proteine micobatteriche PE: localizzazione cellulare e possibile utilizzo per lo sviluppo di un sistema di antigen display

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis, a chronic infectious disease that is responsible for the death of over two million people each year. The genome of Mtb strain H37Rv is made up of 4,411,529 nucleotides and encodes about 3986 proteins. One of the major surprise risen from the genome sequence, published in 1998, is the presence of two large unrelated families of proteins with unknown functions. These protein families are referred to as PE/PPE family of genes. The PE family of Mycobacterium tuberculosis includes 98 proteins which share a highly homologous N-terminus sequence of about 110 amino acids (PE domain). Depending on the C-terminal domain, the PE family can be divided in three subfamilies, the largest of which is the PE_PGRS with 61 members. In this study, we determined the cellular localization of three PE proteins by cell fractionation and immunoelectron microscopy by expressing chimeric epitope-tagged recombinant proteins in Mycobacterium smegmatis. We demonstrate that the PE domains of PE_PGRS33 and PE11 (a protein constituted by the only PE domain) contain the information necessary for cell wall localization, and that they can be used as fusion partners to deliver a sufficiently long C-terminus-linked protein domain on the mycobacterial cell surface. Indeed, we demonstrate that PE_PGRS33 and Rv3097c (a lipase belonging to the PE family) are surface exposed and localize in the mycobacterial cell wall. Moreover, we found that PE_PGRS33 is easily extractable by detergents suggesting its localization in the mycobacterial outer membrane. Beyond defining the cellular localization of these proteins, and a function for their PE domains, these data open the interesting possibility to construct recombinant mycobacteria expressing heterologous antigens on their surface for vaccine purposes