RESUMEN
Lamin B receptor (LBR) is a polytopic protein of the nuclear envelope thought to connect the inner nuclear membrane with the underlying nuclear lamina and peripheral heterochromatin. To better understand the function of this protein, we have examined in detail its nucleoplasmic region, which is predicted to harbor a Tudor domain (LBR-TD). Structural analysis by multidimensional NMR spectroscopy establishes that LBR-TD indeed adopts a classical ß-barrel Tudor fold in solution, which, however, features an incomplete aromatic cage. Removal of LBR-TD renders LBR more mobile at the plane of the nuclear envelope, but the isolated module does not bind to nuclear lamins, heterochromatin proteins (MeCP2), and nucleosomes, nor does it associate with methylated Arg/Lys residues through its aromatic cage. Instead, LBR-TD exhibits tight and stoichiometric binding to the "histone-fold" region of unassembled, free histone H3, suggesting an interesting role in histone assembly. Consistent with such a role, robust binding to native nucleosomes is observed when LBR-TD is extended toward its carboxyl terminus, to include an area rich in Ser-Arg residues. The Ser-Arg region, alone or in combination with LBR-TD, binds both unassembled and assembled H3/H4 histones, suggesting that the TD/RS interface may operate as a "histone chaperone-like platform."
Asunto(s)
Pliegue de Proteína , Receptores Citoplasmáticos y Nucleares/química , Animales , Pollos , Histonas/química , Histonas/genética , Histonas/metabolismo , Proteína 2 de Unión a Metil-CpG/química , Proteína 2 de Unión a Metil-CpG/genética , Proteína 2 de Unión a Metil-CpG/metabolismo , Resonancia Magnética Nuclear Biomolecular/métodos , Estructura Secundaria de Proteína , Estructura Terciaria de Proteína , Receptores Citoplasmáticos y Nucleares/genética , Receptores Citoplasmáticos y Nucleares/metabolismo , Pavos , Receptor de Lamina BRESUMEN
The backbone mobility of the C-terminal domain of procollagen C-proteinase enhancer (NTR PCOLCE1), part of a connective tissue glycoprotein, was determined using 15N NMR spectroscopy. NTR PCOLCE1 has been shown to be a netrin-like domain and adopts an OB-fold such as that found in the N-terminal domain of tissue inhibitors of metalloproteinases-1 (N-TIMP-1), N-TIMP-2, the laminin-binding domain of agrin and the C-terminal domain of complement protein C5. NMR relaxation dynamics of NTR PCOLCE1 highlight conformational flexibility in the N-terminus, strand A and the proximal CD loop. This region in N-TIMP is known to be essential for inhibitory activity against the matrix metalloproteinases and suggests that this region is of equal importance for NTR PCOLCE1, although the specific functional activity of the NTR PCOLCE1 domain is still unknown. Dynamics observed within the structural core of NTR PCOLCE1 that are not observed in N-TIMP molecules suggest that although the two domains have a similar architecture, the NTR PCOLCE1 domain will show different thermodynamic properties on binding and hence the target molecule could be somewhat different from that observed for the TIMPs. ModelFree order parameters show that NTR PCOLCE1 has more flexibility than both N-TIMP-1 and N-TIMP-2.
Asunto(s)
Proteínas de la Matriz Extracelular/química , Glicoproteínas/química , Receptores de Superficie Celular/química , Inhibidores Tisulares de Metaloproteinasas/química , Secuencia de Aminoácidos , Clonación Molecular , Espectroscopía de Resonancia Magnética , Datos de Secuencia Molecular , Receptores de Netrina , Pliegue de Proteína , Precursores de Proteínas/química , Estructura Terciaria de Proteína , Alineación de SecuenciaRESUMEN
The proteins ESAT-6 and CFP-10 have been shown to be secreted by Mycobacterium tuberculosis and Mycobacterium bovis cells, to be potent T-cell antigens, and to have a clear but as yet undefined role in tuberculosis pathogenesis. We have successfully overexpressed both ESAT-6 and CFP-10 in Escherichia coli and developed efficient purification schemes. Under in vivo-like conditions, a combination of fluorescence, circular dichroism, and nuclear magnetic resonance spectroscopy have shown that ESAT-6 contains up to 75% helical secondary structure, but little if any stable tertiary structure, and exists in a molten globule-like state. In contrast, CFP-10 was found to form an unstructured, random coil polypeptide. An exciting discovery was that ESAT-6 and CFP-10 form a tight, 1:1 complex, in which both proteins adopt a fully folded structure, with about two-thirds of the backbone in a regular helical conformation. This clearly suggests that ESAT-6 and CFP-10 are active as the complex and raises the interesting question of whether other ESAT-6/CFP-10 family proteins (22 paired genes in M. tuberculosis) also form tight, 1:1 complexes, and if so, is this limited to their genome partner, or is there scope for wider interactions within the protein family, which could provide greater functional flexibility?