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Proteus mirabilis MR/P fimbrial operon: genetic organization, nucleotide sequence, and conditions for expression
1Department of Medicine, University of Maryland School of Medicine, Baltimore 21201.
Abstract:
Proteus mirabilis, an agent of urinary tract infection, expresses at least four fimbrial types. Among these are the MR/P (mannose-resistant/Proteus-like) fimbriae. MrpA, the structural subunit, is optimally expressed at 37 degrees C in Luria broth cultured statically for 48 h by each of seven strains examined. Genes encoding this fimbria were isolated, and the complete nucleotide sequence was determined. The mrp gene cluster encoded by 7,293 bp predicts eight polypeptides: MrpI (22,133 Da), MrpA (17,909 Da), MrpB (19,632 Da), MrpC (96,823 Da), MrpD (27,886 Da), MrpE (19,470 Da), MrpF (17,363 Da), and MrpG (13,169 Da). mrpI is upstream of the gene encoding the major structural subunit gene mrpA and is transcribed in the direction opposite to that of the rest of the operon. All predicted polypeptides share > or = 25% amino acid identity with at least one other enteric fimbrial gene product encoded by the pap, fim, smf, fan, or mrk gene clusters.
Insights
Proteus mirabilis urinary tract infections are linked to MR/P fimbriae. Researchers sequenced the mrp gene cluster, identifying eight proteins involved in fimbrial production and function.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Proteus mirabilis is a significant cause of urinary tract infections (UTIs).
- This bacterium expresses multiple fimbrial types, including MR/P (mannose-resistant/Proteus-like) fimbriae, which are implicated in virulence.
- Mating type region protein A (MrpA) is the major structural subunit of MR/P fimbriae.
Purpose of the Study:
- To investigate the genetic basis of MR/P fimbriae expression in Proteus mirabilis.
- To determine the complete nucleotide sequence of the mrp gene cluster.
- To identify the proteins encoded by the mrp gene cluster and their potential roles.
Main Methods:
- Isolation and sequencing of the mrp gene cluster from seven Proteus mirabilis strains.
- Bioinformatic analysis to predict the encoded polypeptides and their functions.
- Comparative analysis of predicted amino acid sequences with other known fimbrial gene products.
Main Results:
- The mrp gene cluster spans 7,293 bp and predicts eight distinct polypeptides (MrpI, MrpA, MrpB, MrpC, MrpD, MrpE, MrpF, MrpG).
- Mating type region protein A (MrpA) is the major structural subunit, optimally expressed under specific laboratory conditions (37°C, static Luria broth, 48h).
- The mrpI gene is located upstream of mrpA and transcribed in the opposite direction, suggesting a complex regulatory mechanism.
Conclusions:
- The mrp gene cluster encodes a complete system for MR/P fimbriae biogenesis and function in Proteus mirabilis.
- The predicted polypeptides show significant amino acid identity to other enteric fimbrial proteins, indicating conserved evolutionary pathways.
- Understanding the mrp gene cluster provides insights into the pathogenesis of Proteus mirabilis UTIs and potential therapeutic targets.