Unassuming bodyguards

Altering the structure of peptides can fashion them into loyal and hard-to-beat soldiers of the body's immune syustem

By Rakesh Kalshian
Published: Friday 15 July 1994

EVERY battle has its unsung heroes. Of the impressive array of soldiers that guard animals against foreign invasions, peptides -- small protein molecules composed of several amino acids -- are perhaps the least known.

These unassuming bodyguards can be found patrolling different habitats like insects, frogs, fishes and humans. However, they differ in one important way from the more celebrated soldiers, the white blood corpuscles, in that the former often fail to tell friends from foe. For instance, defensins (peptides found in the human body) can kill not only bacteria but also the oxygen-carrying red blood corpuscles (RBCs).

Now, scientists at the Centre for Cellular and Molecular Biology (CCMB) in Hyderabad have succeeded in divorcing the Jekyll and Hyde sides of a peptide called seminalplasmin residing in the semen of bulls. Which facilitates free movement of sperms and is a microbe-killer.

The seminalplasmin is a large peptide molecule made up of 47 amino acids. The CCMB team, headed by R Nagaraj, have isolated and synthesised a part, comprising 13 amino acids, of this large molecule that kills bacteria but leaves RBCs alone. The peptide segment has been found to exhibit antimicrobial, antifungal and antiviral propeties, says Nagaraj.

Synthesising large molecules like seminalplasmin for making antibiotics is not only difficult but also very expensive, says Nagaraj. With the isolation of a fragment of the molecule, it will now be easy and viable to synthesise them for therapeutical applications.

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