Charakterisierung der Eigenschaften des Mycoplasma arthritidis Superantigens

In the present study the features of the Mycoplasma arthritidis-derived superantigen (MAM) were characterized. The Mycoplasma genome exhibits a characteristically low G + C content. Apart from very few exceptions, the G + C content of Mycoplasma genomes is within the range of 24 to 33 mol%. That' s the reason why the G + C content of MAM was increased from 28% to 47%.First of all the codon usage patterns of Escherichia coli were compared with that of Mycoplasma arthritidis in order to optimize the expression of MAM in E. coli. The codons in question were altered to the optimal codon for E. coli. These steps increased the yield of recombinant MAM.With site-directed mutagenesis (two-step PCR mutagenesis) amino acid residues of potential binding sites of MAM were substituted by alanine or asparagine and glutamine. The functional activity of MAM mutants was examined with HLA-DR transfected L-cells or B-cells and with V beta-transfected T-cells. The results show that histidine residue 14 and aspartic acid 31 are not involved in zinc-dependent binding of MAM to the MHC-class-II-complex. Here it is clearly shown that histidine 58 is an essential residue for the function of MAM. Because substitution of histidine 58 by alanine interrupts presentation of MAM by MHC-class-II. On the other hand glutamic acid residues 28, 30, 39, 40, and 43 are also dispensable, since its substitution don' t interfere with MHC-II- binding. The alanine mutants are still able to interact with MHC-II-complex. However glutamic acid residue 28 plays an important role in interaction with the T-cell receptor. MAM mutant Glu28Ala failed to activate T-cells.Up to now the exact role of zinc ions for MAM dimerization and function need further investigation.As a further interaction partner of MAM CD1-positive cells of the immune system were identified. The results obtained in the present work point out an obviously binding of MAM to CD1a, CD1b, CD1c positive cells. The best interaction of MAM was observed with CD1c.Moreover the data of growth curves presented here indicate a toxic effect of MAM to E. coli. In comparison with Staphylococcal enterotoxin A and Toxic shock syndrome toxin only MAM inhibits growth and viability of E. coli. No protease-activity of MAM could be detected, but the experimental series revealed DNase-activity of MAM. The inhibitory effect of MAM after overexpression on the host bacteria is explained by the fact of DNase-activity displayed by MAM.This outcome suggests the existence of bifunctional proteins with superantigen-activity. In conclusion these proteins are not only potent stimulators of the immune system but also manage enzymatic tasks of the pathogen.In the future the sequence alignment of proteins will promote the discovery of superantigens with interesting features. Once more the unusual characteristics of MAM indicate the existence of proteins with superantigen activity not corresponding to the classical superantigen protein fold.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2005

Author dc:creator

• Diedershagen, Markus

Contributors dc:contributor

• Rink, Lothar

• info:eu-repo/classification/ddc/570
• Biowissenschaften, Biologie
• Antigenpräsentation
• Antigen-Prozessierung
• Antigenrezeptor
• T-Lymphozyt
• T-Lymphozyten-Rezeptor
• MHC
• Mykoplasmen
• Superantigene

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

ger

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-114235%22

OAI record oai:identifier

https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A51989