Chemical shift as a probe of molecular interfaces: NMR studies of DNA binding by the three amino-terminal zinc finger domains from transcription factor IIIA

We report the NMR resonance assignments for a macromolecular protein/DNA complex containing the three amino-terminal zinc fingers (92 amino acid residues) of Xenopus laevis TFIIIA (termed zf1-3) bound to the physiological DNA target (15 base pairs), and for the free DNA. Comparisons are made of the chemical shifts of protein backbone¹ H^N, ¹⁵N,¹³ C and¹³ C and DNA base and sugar protons of the free and bound species. Chemical shift changes are analyzed in the context of the structures of the zf1-3/DNA complex to assess the utility of chemical shift change as a probe of molecular interfaces. Chemical shift perturbations that occur upon binding in the zf1-3/DNA complex do not correspond directly to the structural interface, but rather arise from a number of direct and indirect structural and dynamic effects.     

Point mutants of EHEC intimin that diminish Tir recognition and actin pedestal formation highlight a putative Tir binding pocket

Attachment to host cells by enterohaemorrhagic Escherichia coli (EHEC) is associated with the formation of a highly organized cytoskeletal structure containing filamentous actin, termed an attaching and effacing (AE) lesion. Intimin, an outer membrane protein of EHEC, is required for the formation of AE lesions, as is Tir, a bacterial protein that is translocated into the host cell to function as a receptor for intimin. We established a yeast two-hybrid assay for intimin-Tir interaction and, after random mutagenesis, isolated 24 point mutants in intimin, which disrupted Tir recognition in this system. Analysis of 11 point mutants revealed a correlation between recognition of recombinant Tir and the ability to trigger AE lesions. Many of the mutations fell within a 50-residue region near the C-terminus of intimin. Alanine-scanning mutagenesis of this region revealed four residues (Ser890, Thr909, Asn916 and Asn927) that are critical for Tir recognition. Mapping the sequences of EHEC intimin and Tir onto the crystal structure of the intimin-Tir complex of enteropathogenic E. coli predicts that each of these four intimin residues lies at the intimin-Tir interface and contributes to a pocket that interacts with Ile298 of EHEC Tir. Thus, this genetic approach to intimin function both identified residues critical for Tir binding and demonstrated a correlation between the ability to bind Tir and the ability to trigger actin focusing.     

Immunoelectrophoresis of mycobacterial antigens

Polyvalent antiserum to culture filtrate of H37 Ra M. tuberculosis was raised in rabbits. Monospecific antiserum was raised against M. tuberculosis antigen-5, prepared from the culture filtrates by immunoabsorbent affinity chromatography. On immunoelectrophoresis, antigen-5 demonstrated single precipitin arc against polyvalent and monospecific antisera. The culture filtrate antigen demonstrated multiple precipitin arcs against polyvalent antiserum and single precipitin are against monospecific antiserum. Antigen-5 could be isolated and characterized from the culture filtrate of H37 Ra M. tuberculosis. Immunoelectrophoresis could be one of the method to characterize the mycobacterial antigens prepared in the laboratory.     

Interaction of amino acids with glycyl-glycine transport in the mammalian intestine

In order to investigate a possible interaction between free amino acids and dipeptides during their mucosal uptake in man and monkey, perfusion studiesin vivo and uptake studiesin vitro using labelled and non-labelled dipeptides and amino acids have been carried out. In contrast to the observations of other workers, inhibition of glycyl-glycine uptake was observed with free leucine and methioninc but not with glycine, proline, hydroxyproline or alanine. Leucine and methionine caused inhibition of cytosol glycyl-glycine hydrolase activity, while glycine had no effect. The dipeptide uptake and dipeptide hydrolysis by cytosol enzyme was competitively inhibited by leucine. Although brush border glycyl-glycine hydrolase was also inhibited by leucine, the inhibition was noncompetitive. These data indicate that a few free amino acids can interact with dipeptides during uptake. This interaction might occur either at the transport step or at the stage of intracellular dipeptide hydrolysis. The work reported here was carried out at Wellcome Research Unit, Christian Medical College and Hospital, Vellore 632 004.     

Characterization of epidermal growth factor receptor in testis, epididymis and vas deferens of non-human primates.

The presence of the epidermal growth factor receptor (EGFR) in testis, epididymis and vas deferens of monkeys was demonstrated using a polyclonal antibody (RK2) raised against a peptide-specific sequence of the intracellular domain of the human EGFR. Immunoblotting of membrane preparations revealed a specific band at approximately 170 kDa corresponding to those of controls, A431 and monkey liver cells. Cryostat sections were stained by biotin-streptavidin peroxidase immunocytochemistry. The liver showed positive staining along the basolateral membranes of the hepatocytes lining the sinusoids. The testis showed positive staining indicating the presence of EGFR in Leydig cells, Sertoli cells and peritubular cells. In the epididymis, immunostaining of the EGFR was observed on both the basolateral and the luminal borders of the epididymal epithelium. Immunofluorescence studies revealed a similar pattern of EGFR distribution in the epididymis and indicated that the luminal immunostaining was vesicular. In the vas deferens, positive immunostaining was detected in a pattern very similar to that observed in the epididymis. There was no positive staining in the interstitium of the epididymis or in the smooth muscle cell layers of the vas deferens. The sections of all tissues treated with pre-immune serum were negative. These results suggest that EGF in the primate testis may act at the level of somatic cells. In addition, the basolateral and luminal EGFR staining in the epididymis and vas deferens suggest that these cells respond to an EGF, or EGF-like, source both at the basal, luminal or at both sides of the cells, or that these tissues serve as sites of EGF transcytosis across the epithelium.     

Preparation and characterization of mucilage polysaccharide for biomedical applications

In the present investigation, the polysaccharide/mucilage from waste of Abelmoscus esculentus by modification in hot extraction using two different solvents (Acetone, Methanol) were extracted, characterized and further compared with seaweed polysaccharide for their potential applications. The percentage yield, emulsifying capacity and swelling index of this mucilage were determined. The macro algae and okra waste, gave high % yield (22.2% and 8.6% respectively) and good emulsifying capacity (EC% = 52.38% and 54.76% respectively) with acetone, compared to methanol (11.3% and 0.28%; EC% = 50%) (PH = 7) while swelling index was greater with methanol than acetone extracts respectively. The infrared (I.R.) spectrum of the samples was recorded to investigate the chemical structure of mucilage. Thermal analysis of the mucilage was done with TGA (Thermal Gravimetric Analyzer) and DSC (Differential Scanning Calorimeter) which showed both okra and algal polysaccharide were thermostable hydrogels.