Question

Microbe: mycoplasma pneumoniae

Identify and describe which general secretion system(s) the organism possesses. Next, list at least one other specialized secretion system in the microbe and the effector(s) it secretes. How does this specialized secretion system play a role in the microbe’s life style?

Answer 1

Mycoplasma pneumoniae is a very small bacterium in the class Mollicutes. It is a human pathogen that causes the disease mycoplasma pneumonia, a form of atypical bacterial pneumonial related to cold agglutinin disease.

1. Bacterial pathogens utilizes a multitude of methods to invade mammalian hosts, damage tissue sites and immune system.
2. One essential component of these strategies for many bacterial pathogens is the secretion of protein across phospholipid membranes.
3. Secreted proteins can play many roles in promoting bacterial virulence, from enhancing attachment to eukaryotic cells, to directly intoxicating target cells and distrupting their functions.
4. Dedicated secretion system are used to transport protein out of thr bacterial cell and into the environment or into a recipient cell.
5. However, protein secretion from the bacterial cytoplasmic compartment into other compartments of cells, also occurs.
6. The general secretion(Sec) and twin arginine translocation(Tat) pathway are the bacterial secretion systems most commonly used to transport protein across the cytoplasmic membrane.
7. The Sec and Tat pathway are most highly conserved mechanisms of protein secretion.
8. In Gram negative bacteria, proteins delivered to the cytoplasmic membrane or periplasm of the cell by the Sec or Tat, pathway can be either stay in those compartments, or may be transported outside the cell with the help of another secretion system.

The Sec Secretion pathway

1. The Sec pathway primarily translocates proteins in their unfolded states . This system consist of three parts: a proteins targeting component, a motor protein, and a membrane integrated conducting channel, called the SecYEG translocase.
2. A number of Gram-positive bacteria produce Sec accessory proteins that serve important role in the secretion of specific proteins.
3. Pathogens that use Sec-dependent secretion to transport virulence factor across the cytoplasmic membrane include the Gram-negative bacteria Vibro cholera, Klebsiella pnenumoniae, and Yersinia enterocolitica.
4. Export by the Sec pathway relies on a hydrophobic sigal sequence at the N-terminal of the secreted protein, which is typically 20 amini acid in the length and contain 3 regions: a positive charged amino terminal, a hydrophobic core, and a polar carboxyl-terminate.
5. Protein that will be secreted into the periplasm or outside of the cell by the Sec pathway contain SecB-specific signal sequences,
6. While protein meant to remain in the inner membrane contain a signal recognition particle(SRP)-specific signal sequence.