T cell specific adaptor protein (TSAd) promotes interaction of Nck with Lck and SLP-76 in T cells.

BACKGROUND: The Lck and Src binding adaptor protein TSAd (T cell specific adaptor) regulates actin polymerization in T cells and endothelial cells. The molecular details as to how TSAd regulates this process remain to be elucidated. RESULTS: To identify novel interaction partners for TSAd, we used a scoring matrix-assisted ligand algorithm (SMALI), and found that the Src homology 2 (SH2) domain of the actin regulator Non-catalytic region of tyrosine kinase adaptor protein (Nck) potentially binds to TSAd phosphorylated on Tyr(280) (pTyr(280)) and pTyr(305). These predictions were confirmed by peptide array analysis, showing direct binding of recombinant Nck SH2 to both pTyr(280) and pTyr(305) on TSAd. In addition, the SH3 domains of Nck interacted with the proline rich region (PRR) of TSAd. Pull-down and immunoprecipitation experiments further confirmed the Nck-TSAd interactions through Nck SH2 and SH3 domains. In line with this Nck and TSAd co-localized in Jurkat cells as assessed by confocal microscopy and imaging flow cytometry. Co-immunoprecipitation experiments in Jurkat TAg cells lacking TSAd revealed that TSAd promotes interaction of Nck with Lck and SLP-76, but not Vav1. TSAd expressing Jurkat cells contained more polymerized actin, an effect dependent on TSAd exon 7, which includes interactions sites for both Nck and Lck. CONCLUSIONS: TSAd binds to and co-localizes with Nck. Expression of TSAd increases both Nck-Lck and Nck-SLP-76 interaction in T cells. Recruitment of Lck and SLP-76 to Nck by TSAd could be one mechanism by which TSAd promotes actin polymerization in activated T cells.

Solubility of recombinant Src homology 2 domains expressed in E. coli can be predicted by TANGO.

BACKGROUND: Signalling proteins often contain several well defined and conserved protein domains. Structural analyses of such domains by nuclear magnetic spectroscopy or X-ray crystallography may greatly inform the function of proteins. A limiting step is often the production of sufficient amounts of the recombinant protein. However, there is no particular way to predict whether a protein will be soluble when expressed in E.coli. Here we report our experience with expression of a Src homology 2 (SH2) domain. RESULTS: The SH2 domain of the SH2D2A protein (or T cell specific adapter protein, TSAd) forms insoluble aggregates when expressed as various GST-fusion proteins in Escherichia coli (E. coli). Alteration of the flanking sequences, or growth temperature influenced expression and solubility of TSAd-SH2, however overall yield of soluble protein remained low. The algorithm TANGO, which predicts amyloid fibril formation in eukaryotic cells, identified a hydrophobic sequence within the TSAd-SH2 domain with high propensity for beta-aggregation. Mutation to the corresponding amino acids of the related HSH2- (or ALX) SH2 domain increased the yield of soluble TSAd-SH2 domains. High beta-aggregation values predicted by TANGO correlated with low solubility of recombinant SH2 domains as reported in the literature. CONCLUSIONS: Solubility of recombinant proteins expressed in E.coli can be predicted by TANGO, an algorithm developed to determine the aggregation propensity of peptides. Targeted mutations representing corresponding amino acids in similar protein domains may increase solubility of recombinant proteins.