RESUMO
Cadherins are expressed in tissue-restricted patterns and typically mediate homophilic adhesion. Cadherins also mediate lymphocyte adhesion, providing the opportunity for lymphocyte attachment to parenchymal cells. The best characterized example of lymphocyte adhesion to a tissue-specific cell adhesion molecule, as opposed to a vascular endothelial adhesion molecule, is the interaction between integrin alpha(E)beta(7) on intraepithelial lymphocytes and E-cadherin on epithelial cells. However, the molecular basis for an integrin-cadherin interaction is not well defined. Realization that the cadherin domain adopts a topology similar to the immunoglobulin (Ig) fold suggested that integrin recognition of E-cadherin might be similar to recognition of Ig superfamily ligands. Thus, we modeled domain 1 of human E-cadherin and studied the role of solvent-exposed loops that connect Ig-like core-forming beta strands. Mutational analyses localized the integrin alpha(E)beta(7) recognition site to the top of domain 1 at the face formed by the BC and FG loops, a site distinct from the region recognized in intercellular adhesion molecule (ICAM)-1, -2, and -3, mucosal addressin cell adhesion molecule 1 (MAdCAM-1), vascular cell adhesion molecule 1 (VCAM-1), and fibronectin by their integrin ligands. Moreover, the integrin alpha(E)beta(7) binding site is distinct from the homophilic binding site on E-cadherin. These studies provide a conceptual basis for integrin-cadherin binding and extend the model that an Ig-like fold can serve as a scaffold for recognition.
Assuntos
Caderinas/metabolismo , Células Epiteliais/fisiologia , Integrinas/metabolismo , Leucócitos/fisiologia , Sequência de Aminoácidos , Sítios de Ligação/genética , Mama/citologia , Mama/fisiologia , Caderinas/química , Caderinas/genética , Adesão Celular , Moléculas de Adesão Celular/química , Feminino , Fibronectinas/química , Humanos , Imunoglobulinas/genética , Imunoglobulinas/metabolismo , Modelos Moleculares , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Ligação Proteica/genética , Análise de Sequência de Proteína , Linfócitos T/fisiologiaRESUMO
The identification of structural markers for B12/protein interactions is crucial to a complete understanding of vitamin B12 transport and metabolic reaction mechanisms of B12 coenzymes. Fourier transform infrared spectroscopy can provide direct measurements of changes in the side chains and corrin ring resulting from B12/protein interactions. Using FTIR spectroscopy in various solvent systems, we have identified structural markers for corrinoids in the physiological state. We assign the major band (denoted B), which occurs at ca. 1630 cm-1 in D2O and ca. 1675 cm-1 in ethanol, to the amide I C=O stretching mode of the propionamide side chains of the corrin ring. The lower frequency of band B in D2O versus ethanol is due to the greater hydrogen-bonding properties of D2O that stabilize the charged amide resonance form. Since the propionamides are known to be important in protein binding, band B is a suitable marker for monitoring the interaction of these side chains with proteins. We assign bands at ca. 1575 and 1545 cm-1 (denoted C and D) as breathing modes of the corrin ring on the basis of the bands' solvent independence and their sensitivity to changes in axial ligation. As the sigma-donating strength of the axial ligands increases, the frequencies of bands C and D decrease, possibly indicating a lengthening of the corrin conjugated system. Band A, the known cyanide stretching frequency at ca. 2130 cm-1, probes the cobalt-carbon distance in cyanocorrinoids. As the frequency of band A increases, the cobalt-carbon bond strength should decrease.