Professor Israel Pecht
Recognition and Signaling by Immunoreceptors
We aim at resolving, in molecular and quantitative terms the mechanisms of recognition performed by the multichain immunorecognition receptors (MIRRs) and the mechanisms which couple them to the respective cellular response. We perform direct measurements, by fluorescence methods, of peptide binding in homogeneous solutions to recombinant human and mouse class I molecules. These yield detailed thermodynamic and kinetic insights into the mutual interactions among the components of these ternary complexes: Assembly of mouse H2-Kd and H2-Kb as well as human A-2 ternary complexes with a range of specific peptides was shown to exhibit allosteric control; while peptide binding to the heterodimer enhances -2m binding to the heavy chain; peptide's affinity to the heavy chain drastically increases upon -2m binding. These ternary complexes of class I MHC molecules with peptides are further modified with fluorescent probles and employed for interactions, as ligands, with the T-cell antigen receptor on living cells.
The main model system employed for cell stimulation by a MIRR family member is that of mast cells by the type 1 Fc- receptor (Fc--RI). We have discovered that immobilization of these receptors is one requirement for production of the stimulus. This most probably is a more general constraint for most, if not all MIRRs and is rationalized by the need for producing a "transdusosome", i.e. a nucleus of binding sites on the receptors' cytosolic tails for downstream components of the signaling cascade. We study the biochemical processes of the FcRI coupling cascade, in particular we pursue the control of the response to the FcRI by two different mechanisms: The first is by a glycoprotein discovered in our lab and named Mast cell Function-associated Antigen(MAFA) shown to have binding capacity to terminal manosides. In MAFA's intracellular tail, a sequence is present which is analogous to that of Immunoreceptors Tyrosine-based Inhibitory Motifs (ITIM). Recently, we have shown that two different enzymes are mediating the inhibitory action: a protein tyrosine phosphatase (SHP-2) and an inositol phospatase (SHIP). The inositol mechanism of these processes are investigated. Another control mechanism of the cellular response to the Fc--RI discovered in our lab is that exerted by the anaphylotoxin C3a and peptides derived from it. Possible therapeutic uses of this discovery are being studied.
Electron Transfer Mechanisms Through Protein Matrices
The mechanism of electron transfer via polypeptide matrices is investigated in two types of systems:
- 1) Using single-site mutations of the electron-carrier, single blue copper protein azurin.
- 2) In the multi-centered redox enzymes, ascorbate oxidase, nitrous oxide reductase as well as in iron or copper nitrite reductases.
List of Publications