Novel synthetic lipopeptides derived from Mycoplasma hyorhinis upregulate calpastatin in SH-SY5Y neuroblastoma cells and induce a neuroprotective effect against amyloid-ß-peptide toxicity.

Previously, we showed that contamination of SH-SY5Y neuroblastoma cells by Mycoplasma hyorhinis strains NDMh and MCLD leads to increased levels of calpastatin (the endogenous, specific inhibitor of the Ca2+-dependent protease calpain), resulting in inhibition of calpain activation. We have found that the increased calpastatin level is promoted by the lipoprotein fraction (MhLpp) of the mycoplasmal membrane. Here, we present MhLpp-based novel synthetic lipopeptides that induce upregulation of calpastatin in SH-SY5Y neuroblastoma cells, leading to protection of the treated cells against Ca2+/amyloid-ß-peptide toxicity. These lipopeptides present a new class of promising agents against calpain-induced cell toxicity.

Structural insights into the extracytoplasmic thiamine-binding lipoprotein p37 of Mycoplasma hyorhinis.

The Mycoplasma hyorhinis protein p37 has been implicated in tumorigenic transformation for more than 20 years. Though there are many speculations as to its function, based solely on sequence homology, the issue has remained unresolved. Presented here is the 1.6-A-resolution refined crystal structure of M. hyorhinis p37, renamed the extracytoplasmic thiamine-binding lipoprotein (Cypl). The structure shows thiamine pyrophosphate (TPP) and two calcium ions are bound to Cypl and give the first insights into possible functions of the Cypl-like family of proteins. Sequence alignments of Cypl-like proteins between several different species of mycoplasma show that the thiamine-binding site is likely conserved and structural alignments reveal the similarity of Cypl to various binding proteins. While the experimentally determined function of Cypl remains unknown, the structure shows that the protein is a TPP-binding protein, opening up many avenues for future mechanistic studies and making Cypl a possible target for combating mycoplasma infections and tumorigenic transformation.

Recognition of Mycoplasma hyorhinis by CD99-Fc molecule.

The human CD99 protein is expressed on many cell types and is mostly abundant on lymphocytes and on several tumors. Different functions were attributed to the CD99 receptor, including adhesion, apoptosis and activation. However, until now the only ligand suggested to be recognized by CD99 was CD99 itself. In order to identify possible new CD99 ligands we constructed a CD99 protein fused to human IgG1. Surprisingly, a pronounced specific staining of melanoma cell lines that were infected with mycoplasmas was observed whereas clean cells were not recognized. Staining was specific, as other fusion proteins did not recognize the mycoplasma-infected cells. Sequencing of the 23s-16s region revealed that the contaminating agent is Mycoplasma hyorhinis. The CD99 interaction with M. hyorhinis was direct since it was blocked by anti-CD99 monoclonal antibody and by M. hyorhinis. It was also strain-specific as other mycoplasmas were not recognized. Our results show that CD99 interacts with a novel ligand of M. hyorhinis.