Definition

Bacterial peptides are protein fragments which are either part of a bacterium or produced by a bacteria¹.

Classification

Different classes of peptides are produced by bacteria. Some examples include, antibiotics, enterotoxins, flagellar proteins, lipoproteins and various enzymes¹.

Structural Characteristics

Structural characteristics of some bacterial peptides are described below-

A)      Malaria merozoite surface peptide (MSP-1): It is synthesized as a large precursor on the surface of the bacterium Plasmodium falciparum.  Proteolytic cleavage results in the production of a 19 KDa product whose tertiary structure is maintained by disulphide bridges².

B)     Giardia variable surface protein: This peptide is the specific conserved region of the Giardia variable surface proteins (VSPs) that are cysteine rich zinc finger proteins. VSPs differ in size and sequence, they are characterized by this highly conserved C-terminal membrane spanning region, a hydrophilic cytoplasmic tail with a conserved five amino acid CRGKA signature sequence^3,4.

C)    P.falciparum liver stage antigen 3: The protein is 200Kda and is highly conserved among parasites from different geographic regions⁵.

Mode of action

A)     MSP-1 is known to trigger antibody response by CD4 helper T cells. It is likely that these cells bind to the C-terminal domain of MSP-1².

B)     VSPs have a conserved hydrophilic amono acid trail that is palmitoyted by palmityl tranferases upon which they are activated^3,4.

C)    P. falciparum liver stage antigen 3 is a potent antigen that is recongnized by T cells⁵.

Functions

A)     MSP-1 is a vaccine candidate for Plasmodium falciparum infection. It triggers a CD-4 T cell response².

B)     VSPs are necessary for survival in the environment and host infection^3,4.

C)    P.falciparum stage antigen 3 is also a good candidate vaccine as it activates both T and B cell responses⁵.

References

1.     Gitai Z (2005). "The new bacterial cell biology: moving parts and subcellular architecture". Cell, 120 (5): 577–86.

2.     Stuart JQ and Jean L (2001). Different regions of the malaria merozoite surface protein 1 of Plasmodium chabaudi elicit distinct T-cell and antibody isotype responses. Infect Immun, 69(4): 2245–2251.

3.     Davids BJ, Reiner DS, Birkeland SR, Preheim SP, Cipriano MJ, McArthur AG, Gillin FD (2006). A New Family of Giardial Cysteine-Rich Non-VSP Protein Genes and a Novel Cyst Protein. PLoS ONE, 20,1:e44.

4.     Touz MC, Conrad JT, Nash TE (2005). A novel palmitoyl acyl transferase controls surface protein palmitoylation and cytotoxicity in Giardia lamblia. Mol Microbiol., 58 (4), 999-1011.

5.     Jean-Pierre S, Blanca LP, Karima B, Pierra D, Pierra D (2001). DNA Immunization by Plasmodium falciparum liver-stage antigen 3 induces protection against Plasmodium yoelii Sporozoite challenge. Infect Immun., 69, 1202–1206.