title: Homodimerization and heterodimerization of minimal zinc(II)-binding-domain peptides of T-cell proteins CD4, CD8alpha, and Lck.
abstract: Metal-mediated protein oligomerization is an emerging mode of protein-protein interaction. The C-terminal cytosolic domains of T-cell coreceptors CD4 and CD8alpha form zinc-bridged heterodimers with the N-terminal region of the kinase Lck, with each protein contributing two cysteinate ligands to the complex. Using size exclusion chromatography, (1)H NMR, and UV/visible absorption spectroscopy with cobalt(II) as a spectroscopic probe, we demonstrate that small peptides derived from these regions form metal-bridged heterodimers but also homodimers, in contrast to previous reports. The Lck-CD4 and Lck-CD8alpha cobalt(II)-bridged heterodimer complexes are more stable than the corresponding (Lck)(2)cobalt(II) complex by factors of 11 +/- 4 and 22 +/- 9, respectively. These studies were aided by the discovery that cobalt(II) complexes with a cobalt(II)(-Cys-X-X-Cys-)(-Cys-X-Cys-) chromophore show unusual optical spectra with one component of the visible d-d ((4)A(2)-to-(4)T(1)(P)) transition red-shifted and well separated from the other components. These results provide insights into the basis of specificity of metal-bridged complex formation and on the potential biological significance of metal-bridged homodimers in T-cells.
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes, Digestive & Kidney Disorders, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Alisa M
authors.initials: AM
authors.lastname: Davis
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Berg
mesh_terms: D000595:Amino Acid Sequence; D015704:CD4 Antigens / Q000737:chemistry / Q000378:metabolism*; D016827:CD8 Antigens / Q000737:chemistry / Q000378:metabolism*; D002845:Chromatography; D003035:Cobalt / Q000378:metabolism; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D013601:T-Lymphocytes / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
chemical_list: D015704:CD4 Antigens; D016827:CD8 Antigens; C409469:CD8 antigen, alpha chain; D010455:Peptides; D003035:Cobalt; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D015032:Zinc