Structure-function relations of variant and fragment nisins studied with model membrane systems

Area of Science:

• Microbiology
• Biochemistry
• Biophysics

Background:

• Nisin is a lantibiotic produced by Lactococcus lactis subsp. lactis, known for its antimicrobial activity against Gram-positive bacteria.
• Nisin targets the cytoplasmic membrane, but the precise structural determinants of its membrane interaction and permeabilization are not fully understood.

Purpose of the Study:

• To investigate the structural aspects of nisin that facilitate membrane interaction and permeabilization.
• To elucidate the role of specific residues and charge distributions in nisin's antimicrobial mechanism.

Main Methods:

• Utilized planar lipid bilayers and liposomes to study nisin and its variants.
• Employed proteolytic fragments and site-directed variants (I30W, K12L, H27K) of nisin.
• Measured phospholipid mobility, membrane capacitance, electrical conductance, and calcein release.

Main Results:

• N-terminal fragments (N1-12, N1-20) showed minimal membrane effects.
• The I30W nisin A variant mimicked native nisin's ability to reduce lipid mobility, decrease capacitance, increase conductance, and release calcein.
• Charge substitutions (K12L, H27K) influenced ion flow, with K12L showing stronger effects than I30W, and H27K showing weaker effects.
• Nisin and variants showed enhanced calcein release from negatively charged phospholipids, suggesting electrostatic attraction drives initial membrane association.

Conclusions:

• Specific residues, particularly intramembrane charged residues, play a crucial role in controlling ion flow through nisin-interacting membranes.
• Electrostatic interactions are important for the initial association of nisin with bacterial membranes.
• The findings provide insights into the mechanism of nisin's antimicrobial action at the membrane level.