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M P Regalado

Publications and source records attributed to M P Regalado.

4 recordsLinked to original sources
PubMed2001

Intersubunit cooperativity in the NMDA receptor.

Opening of the NMDA receptor channel requires simultaneous binding of glutamate and glycine. Although the binding sites for each agonist are in different subunits, the presence of one agonist influences the binding of the other. We have localized regions in the S1 binding domain of both subunits required for the transmission of allosteric signals from the glutamate binding NR2A subunit to the glycine binding NR1 subunit. Three-dimensional modeling indicates that these segments are not directly involved in ligand binding, but likely form solvent-accessible loops protruding out of the binding pocket, making them suitable to relay interactions between adjacent subunits. Thus, these segments mediate negative allosteric coupling between the two subunit types that form the NMDA receptor.

Allosteric Regulation↗
PubMed1998

Glycine-independent NMDA receptor desensitization: localization of structural determinants.

In studying chimeras of NR2A and NR2C subunits of the NMDA receptor, we have found that glycine-independent desensitization depends on two regions of the extracellular N-terminal domain. One corresponds to a stretch of approximately 190 amino acids preceding the glutamate-binding domain S1. The other localizes at the interface between the N-terminal segment and the first transmembrane domain of NR2A subunits and involves A555 and S556. Both regions support desensitization in the absence of the other with different time courses. Desensitization did not develop with time in receptors containing the entire N-terminal region of NR2C. The introduction of A555 into the corresponding position of NR2C subunits enabled the receptors to manifest time-dependent increase in desensitization. Thus, this determinant behaves as an allosteric effector for glycine-independent desensitization.

Allosteric Regulation↗
PubMed1996

Identification of an essential region for internal initiation of translation in the aphthovirus internal ribosome entry site and implications for viral evolution.

Translation of aphthovirus RNA is initiated at an internal ribosome entry site (IRES) element, preceding the first functional AUG initiation codon. The effect of mutations at the base of domain 3 of the aphthovirus IRES on translation activity has been analyzed by site-directed mutagenesis and expression of bicistronic RNAs in transfected cells. The results have shown that the enhanced IRES activity associated with a single pyrimidine transition fixed in a persistent aphthovirus variant (E. Martínez-Salas, J. C. Sáiz, M. Dávila, G. J. Belsham, and E. Domingo, J. Virol. 67:3748-3755, 1993) is base specific. Mutations predicted to destabilize the base of domain 3 were detrimental to IRES function, but subsequent restoration of the RNA structure gave rise to fully competent IRES. In contrast, single or multiple mutations that did not affect predicted helical structures modified the relative efficiency of translation by at most 10-fold, suggesting that primary sequence also plays a role in IRES activity. A correlation between the energy of stabilization of the IRES structure and the efficiency of translation has been noted. None of the 15 mutations studied reached a level of initiation of translation comparable to that of the IRES from the persistent variant. The results indicate a critical participation of the base of domain 3 in the activity of the aphthovirus IRES, with a strong effect of secondary or higher-order structures and minor effects of primary structure.

Animals↗