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Gonococcal pili. Primary structure and receptor binding domain
Abstract:
The complete amino acid sequence of pilin from gonococcal strain MS11 and the sequence of constant and variable regions from strain R10 pilin have been determined in order to elucidate the structural basis for adherence function, antigenic diversity, and polymeric structure. The MS11 pilin sequence consists of 159 amino acids in a single polypeptide chain with two cysteines in disulfide linkage and serine-bonded phosphate residues. TC-2 (31-111), a soluble monomeric pilus peptide prepared by arginine-specific digestion, bound human endocervical, but not buccal or HeLa cells and therefore is postulated to encompass the receptor binding domain. Variable regions of CNBr-3 appear to confer antigenic diversity and comprise segments in which changes in the position of charged residues occur in hydrophilic, beta-turns. Residues 2-21 and 202-221 of gonococcal pilins and lower eucaryotic actins, respectively, exhibit 50% homology. When these residues are arranged at intervals of 100 degrees of arc on "helical wheels," the identical amino acids comprise a hydrophobic face on one side of the helix. This observation, the hydrophobic character of this region and the tendency for TC-1 (residues 1-30) to aggregate in water, suggest that this stretch interacts with other subunits to stabilize polymeric structure.
Insights
Structural analysis of gonococcal pilin reveals key regions for cell adherence and immune evasion. Understanding pilin structure aids in developing strategies against Neisseria gonorrhoeae.
Area of Science:
- Microbiology
- Structural Biology
- Immunology
Background:
- Neisseria gonorrhoeae uses pili for host cell attachment and immune system evasion.
- Pilin, the major subunit of gonococcal pili, exhibits significant antigenic diversity.
Purpose of the Study:
- To determine the complete amino acid sequence of gonococcal pilin.
- To elucidate the structural basis of pilin's adherence function, antigenic diversity, and polymeric structure.
Main Methods:
- Amino acid sequencing of pilin from gonococcal strains MS11 and R10.
- Preparation of a soluble monomeric pilus peptide (TC-2) via arginine-specific digestion.
- Analysis of conserved and variable regions, including homology with eukaryotic actins.
Main Results:
- The MS11 pilin sequence comprises 159 amino acids with disulfide-linked cysteines and phosphoserine residues.
- The TC-2 peptide (residues 31-111) binds to human endocervical cells, indicating its role in receptor binding.
- Variable regions (CNBr-3) contribute to antigenic diversity, featuring charged residue changes in hydrophilic segments and beta-turns.
- Significant homology (50%) was found between gonococcal pilin residues 2-21 and eukaryotic actin residues 202-221, forming a hydrophobic face on helical wheels.
- The N-terminal region (TC-1, residues 1-30) shows aggregation properties, suggesting its involvement in stabilizing pilus structure.
Conclusions:
- The study identifies specific pilin regions responsible for cell adherence, antigenic variation, and pilus assembly.
- Structural insights into pilin provide a foundation for understanding gonococcal pathogenesis and developing targeted interventions.