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Protein D, an immunoglobulin D-binding protein of Haemophilus influenzae: cloning, nucleotide sequence, and
1Department of Medical Microbiology, University of Lund, Malmö General Hospital, Sweden.
Abstract:
The gene for protein D, a membrane-associated protein with specific affinity for human immunoglobulin D, was cloned from a nontypeable strain of Haemophilus influenzae. The gene was expressed in Escherichia coli from an endogenous promoter, and the gene product has an apparent molecular weight equal to that of H. influenzae protein D (42,000). The complete nucleotide sequence of the gene for protein D was determined, and the deduced amino acid sequence of 364 residues includes a putative signal sequence of 18 amino acids containing a consensus sequence, Leu-Ala-Gly-Cys, for bacterial lipoproteins. The sequence of protein D shows no similarity to those of other immunoglobulin-binding proteins. Protein D is the first example of immunoglobulin receptors from gram-negative bacteria that has been cloned and sequenced.
Insights
Researchers cloned the gene for protein D, a unique Haemophilus influenzae protein that binds human immunoglobulin D. This study details its nucleotide sequence and protein structure, revealing no similarity to other immunoglobulin-binding proteins.
Area of Science:
- Microbiology
- Molecular Biology
- Immunology
Background:
- Haemophilus influenzae is a pathogen that can cause various infections.
- Protein D is a surface protein of H. influenzae with a known affinity for human immunoglobulin D.
- The genetic basis and detailed structure of Protein D were not fully understood.
Purpose of the Study:
- To clone and characterize the gene encoding Protein D from Haemophilus influenzae.
- To determine the nucleotide and amino acid sequence of Protein D.
- To investigate the structural features and potential function of Protein D.
Main Methods:
- Cloning of the protein D gene from a nontypeable H. influenzae strain.
- Expression of the cloned gene in Escherichia coli.
- Determination of the complete nucleotide sequence.
- Deduction of the amino acid sequence and analysis of its features.
Main Results:
- The gene for Protein D was successfully cloned and expressed in E. coli.
- The gene product showed an apparent molecular weight of 42,000.
- The complete nucleotide sequence was determined, revealing a 364-residue amino acid sequence.
- A putative signal sequence for bacterial lipoproteins was identified.
- Protein D sequence showed no similarity to other known immunoglobulin-binding proteins.
Conclusions:
- Protein D represents a novel class of immunoglobulin receptors in Gram-negative bacteria.
- The cloning and sequencing provide a foundation for further studies on Protein D's function and structure.
- This work is the first to clone and sequence an immunoglobulin receptor from a Gram-negative bacterium.