Homodimerization and Heterodimerization of Minimal Zinc(II)-Binding-Domain Peptides of T-Cell Proteins CD4, CD8α, and Lck

• Published in: Journal of the American Chemical Society Vol. 131; no. 32; pp. 11492 - 11497
• Main Authors: Davis, Alisa M., Berg, Jeremy M.
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 19.08.2009; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; CYTOPLASMIC TAIL; ZINC-DEFICIENCY; SPECIFICITY; TYROSINE KINASE; RESOLUTION; P56(LCK); GENERATION; IMMUNOLOGICAL SYNAPSE; BINDING; EXPRESSION
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja9028928

Metal-mediated protein oligomerization is an emerging mode of protein−protein interaction. The C-terminal cytosolic domains of T-cell coreceptors CD4 and CD8α 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, 1H 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-CD8α cobalt(II)-bridged heterodimer complexes are more stable than the corresponding (Lck)2cobalt(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 (4A2-to-4T1(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.