On the function of a membrane protein insertase in developing cells of Bacillus subtilis

ITQB PhD Seminars

Title: On the function of a membrane protein insertase in developing cells of Bacillus subtilis

Speaker: Maria Luísa Corte

Laboratory: Microbial Development

Abstract

Spore differentiation in the rod-shaped Bacillus subtilis and related bacteria takes place in a cell divided in two unequal compartments. The smaller, or forespore, will become the future spore. The larger, or mother cell, nurtures the developing spore but lyses at the end of the process to release the mature spore into the environment. Each of these two cells has a copy of the genome, and deploys specific but interconnected programs of gene expression, that are also sensitive to morphological cues that signal completion of key cellular structures. This means that successive waves of gene expression in one cell or the other are activated in a coordinated manner and in register with the course of morphogenesis. Soon after the initial asymmetric division of the rod cell that produces the polar forespore and the mother cell, this later cell starts to engulf the forespore. This is a process akin to phagocytosis, whereby the forespore is converted into a free protoplast, floating within the cytoplasm of the mother cell, and separated from it by a double membrane system derived from the division septum. Engulfment completion is a morphological signal for the activation of a transcription factor in the forespore, called G, which governs the late stages of differentiation in this cell. Remarkably, activation of G also requires expression of a mother cell-specific operon that codes for a novel type of secretion system, called A. Evidence suggests that this system in fact forms a pore spanning the intermembrane space between the two cells, much in the way of gap junctions do in certain eukaryotic cells. Evidence also suggests that this transporter operates at the expense of ATP hydrolysis to keep the metabolic potential in the forespore when, following engulfment completion, it becomes isolated from the external medium. Thus, the A system functions as an umbilical cord, allowing the mother cell to feed the developing spore. Evidence also indicates that assembly of this mother cell-to-forespore channel requires the action of a membrane protein insertase called J. The J protein in turn, is a member of a large family of insertase found in archaea, bacteria and eukaryotes. A striking analogy is the role of J orthologs in the insertion of chromosomally-encoded genes in the inner membranes of mitochondria and chloroplasts. To begin elucidating the mechanism by which J operates in the activation of G, we have overproduced and purified the protein. We will present a genetic and biochemical characterization of the J membrane protein insertase, with implications for its role in the activation of G in developing cells of B. subtilis.

Short CV

Since October 2002: PhD student (SFRH / BD / 6489 / 01) at Microbial Development group, ITQB- UNL, Oeiras, Portugal. Research Project: The role of the SpoIIIJ translocase in the activation of the G subunit of the RNA polymerase during sporulation in Bacillus subtilis. Supervisor: Prof. Adriano O. Henriques.
2001/2002 - Scientific Initiation Grant (BIC). Microbial Development Group ITQB- UNL, Oeiras, Portugal.
2000/2001 - Research assistant. Swammerdam Institute for Life Sciences –Molecular Cytology Section, University of Amsterdam, Amsterdam, The Netherlands.
Graduation (Licenciatura) in Biologia Microbiana e Genética, Universidade de Lisboa, Lisboa, Portugal.