Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0162871 (abdominal aortic aneurysm)
 8,664 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To further investigate the ways in which proteins respond to changes in the length of the polypeptide chain, a series of 32 insertions and five deletions were made within nine different alpha-helices of T4 lysozyme. In most cases, the inserted amino acid was a single alanine, although in some instances up to four residues, not necessarily alanine, were used. Different insertions destabilized the protein by different amounts, ranging from approximately 1 to 6 kcal/mol. In one case, no protein could be obtained. An "extension" mutant in which the carboxy terminus of the molecule was extended by four alanines increased stability by 0.3 kcal/mol. For the deletions, the loss in stability ranged from approximately 3 to 5 kcal/mol. The structures of six insertion mutants, as well as one deletion mutant and the extension mutant, were determined, three in crystal forms nonisomorphous with wild type. In all cases, including previously described insertion mutants within a single alpha-helix, there appears to be a strong tendency to preserve the helix by translocating residues so that the effects of the insertion are propagated into a bend or loop at one end or the other of the helix. In three mutants, even the hydrophobic core was disrupted so as to permit the preservation of the alpha-helix containing the insertion. Translocation (or "register shift") was also observed for the deletion mutant, in this case a loop at the end of the helix being shortened. In general, when translocation occurs, the reduction in stability is only moderate, averaging 2.5 kcal/mol. Only in the most extreme cases does "bulging" or "looping-out" occur within the body of an alpha-helix, in which case the destabilization is substantial, averaging 4.9 kcal/mol. Looping-out can occur for insertions close to the end of a helix, in which case the destabilization is less severe, averaging 2.6 kcal/mol. Mutant A73-[AAA] as well as mutants R119-[A] and V131-[A], include shifts in the backbone of 3-6 A, extending over 20 residues or more. As a result, residues 114-142, which form a "cap" on the carboxy-terminal domain, undergo substantial reorganizations such that the interface between this "cap" and the rest of the protein is altered substantially. In the case of mutant A73-[AAA], two nearby alpha-helices, which form a bend of approximately 105 degrees in the wild-type structure, reorganize in the mutant structure to form a single, essentially straight helix. These structural responses to mutation demonstrate the plasticity of protein structures and illustrate ways in which their three-dimensional structures might changes during evolution.
 ...
PMID:Protein structural plasticity exemplified by insertion and deletion mutants in T4 lysozyme. 897 49

To characterize the roles played by surface-charged residue Asp44 in the structure stability of horse heart myoglobin, the code of Asp44, GAT, in the gene of horse heart myoglobin was changed into AAA for Lys by PCR site-directed mutagenesis. The mutant gene was ligated into PstI/BamHI-cut pGYM and the resulting plasmid was transformed into E. coli BL21. The mutant protein (D44K) was expressed in BL21 successfully. The bacteria containing mutant myoglobin were treated with lysozyme. Then the mutant protein was purified by ammonium sulfate precipitation, ion-exchange chromatography and gel filtration. Circular dichroism spectra were employed to monitor the kinetic behaviors of wild-type and mutant myoglobins' denaturation at different pHs or upon heating, and the "two-state" model was used to simulate the kinetic process of wild-type and mutant myoglobins' denaturation upon heating to determine the unfolding thermodynamic parameters of Mb and its mutant (D44K). The results show that the mutation of the surface-charged residue Asp44 to Lys44 can increase the protein's stability on its resistance to heat, resulting in the increase in the protein's denaturing mid-temperature by about 4 degrees C, from 71.9 to 75.1 degrees C, but shows little effect on its resistance to acid denaturation.
 ...
PMID:[Probe of the effect of Asp44 on the stability of myoglobin by circular dichroism spectropolarimeter]. 1847 38

Bacterial pathogens use a range of protein secretion systems to colonize their host. One recent addition to this arsenal is the type VI secretion system (T6SS), which is found in many Gram-negative bacteria. The T6SS involves 12-15 components, including a ClpV-like AAA(+) ATPase. Moreover, the VgrG and Hcp components have been proposed to form a puncturing device, based on structural similarity to the tail spike components gp5/gp27 and the tail tube component gp19 of the T4 bacteriophage, respectively. Another T6SS component shows similarity to a T4 phage protein, namely gp25. The gp25 protein has been proposed to have lysozyme activity. Other T6SS components do not exhibit obvious similarity to characterized T4 phage components. The genome of Pseudomonas aeruginosa contains three T6SS gene clusters. In each cluster a gene encoding a putative member of the gp25-like protein family was identified, which we called HsiF. We confirmed this similarity by analysing the structure of the P. aeruginosa HsiF proteins using secondary and tertiary structure prediction tools. We demonstrated that HsiF1 is crucial for the T6SS-dependent secretion of Hcp and VgrG. Importantly, lysozyme activity of HsiF proteins was not detectable, and we related this observation to the demonstration that HsiF1 localizes to the cytoplasm of P. aeruginosa. Finally, our data showed that a conserved glutamate, predicted to be required for proper HsiF folding, is essential for its function. In conclusion, our data confirm the central role of HsiF in the T6SS mechanism, provide information on the predicted HsiF structure, and call for reconsideration of the function of gp25-like proteins.
 ...
PMID:Structure-function analysis of HsiF, a gp25-like component of the type VI secretion system, in Pseudomonas aeruginosa. 2187 4