The primary structure of the cytotoxin restrictocin

Area of Science:

• Biochemistry
• Molecular Biology
• Proteomics

Background:

• Cytotoxins are proteins that exhibit toxicity to cells.
• Restrictocin is a cytotoxin with potential biological activity.
• Understanding the primary structure of cytotoxins is crucial for elucidating their function and mechanism of action.

Purpose of the Study:

• To determine the complete amino acid sequence of the cytotoxin restrictocin.
• To elucidate the structural features of restrictocin, including disulfide bridges.
• To compare the sequence of restrictocin with other known cytotoxins.

Main Methods:

• Automated Edman degradation of the intact and modified restrictocin molecule.
• Chemical cleavage of restrictocin using cyanogen bromide and BNPS-skatole.
• Enzymatic cleavage of restrictocin using trypsin.
• Sequence analysis and homology comparison.

Main Results:

• The complete amino acid sequence of restrictocin, a single polypeptide chain of 149 residues, was determined.
• The calculated relative molecular mass of restrictocin is 16836.
• Restrictocin possesses two disulfide bridges: Cys5-Cys147 and Cys75-Cys131.
• The amino acid sequence of restrictocin exhibits 86% homology with the cytotoxin alpha-sarcin.

Conclusions:

• The primary structure of restrictocin has been fully elucidated.
• Restrictocin shares significant sequence similarity with alpha-sarcin, suggesting potential functional or evolutionary links.
• The identified disulfide bridges are key structural elements of restrictocin.