PubMed · 10610576
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
D M Hillis. 1999-12-03. Predictive evolution.. https://doi.org/10.1126/science.286.5446.1866
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
Deficient activity of human lysosomal hydrolase, acid sphingomyelinase (ASM), results in the neuronopathic (type A) and non-neuronopathic (type B) forms of Niemann-Pick disease (NPD). A deficiency of ASM is known to deprive lymphoblasts of their response to apoptotic induction by X-ray irradiation. To elucidate the genetic heterogeneity of apoptotic induction in NPD cells, we investigated radiation-induced apoptosis of lymphoblasts in patients with type A (genotype: IVS3-2A-G/IVS3-2A-G) and type B (genotype: S436R/S436R) NPD. Epstein-Barr virus (EBV)-transformed lymphoblasts established from a patient with type A NPD, a patient with type B NPD and a normal control were irradiated with 20 Gy and incubated for 24 h. The cells were harvested and the morphological features of apoptosis were observed with DNA-specific fluorochrome bis-benzimide. Exposure of lymphoblasts to 20 Gy of radiation resulted in 25-30% apoptosis of total cells in normal lymphoblasts, 8-9% apoptosis in type A NPD and 20-27% apoptosis in type B NPD. The radiation-induced apoptotic response in the lymphoblasts of type A NPD was significantly different from that of the normal lymphoblasts (P<0.0005). On the other hand, the radiation-induced apoptotic response in type B NPD was not markedly different from that in normal lymphoblasts (P=0.624). In the patient with type B NPD, the signaling pathway for radiation-induced apoptosis was preserved in lymphoblasts, which suggests that the extent of cell signaling system disturbance due to ASM deficiency may be related to the phenotypes in types A and B NPD.
The biosynthesis of cephalosporins is catalyzed by deacetoxycephalosporin C synthase (DAOCS). Based on computational, biochemical, and structural analyses, it has been proposed that modification of the C-terminus of DAOCS might be a constructive strategy for engineering improvement in enzyme activity. Therefore, five hydrophilic residues namely N301, Y302, N304, R306, and R307 located in proximity to the C-terminus of Streptomyces clavuligerus DAOCS (scDAOCS) were selected and each substituted with a hydrophobic leucine residue. Substitutions at positions 304, 306, and 307 created mutant scDAOCSs with improved efficiencies in penicillin analog conversion up to 397%. And since it has been previously advocated that the C-terminus is crucial for guiding substrate entry, a truncated mutant DAOCS was constructed to assess its involvement. The truncation of the C-terminus at position 310 in the wild-type scDAOCS resulted in reduction of indiscriminate conversion of penicillin analog but this defect was compensated by the replacement of asparagine with leucine at position 304.
CCR6 is the receptor for the chemokine MIP-3 alpha/CCL20. Almost all chemokine receptors contain cysteine residues in the N-terminal domain and in the first, second, and third extracellular loops. In this report, we have studied the importance of all cysteine residues in the CCR6 sequence using site-directed mutagenesis and biochemical techniques. Like all G protein-coupled receptors, mutating disulfide bond-forming cysteines in the first (Cys118) and second (Cys197) extracellular loops in CCR6 led to complete elimination of receptor activity, which for CCR6 was also associated with the accumulation of the receptor intracellularly. Although two additional cysteines in the N-terminal region and the third extracellular loop, which are present in almost all chemokine receptors, are presumed to form a disulfide bond, this has not been demonstrated experimentally for any of these receptors. We found that mutating the cysteines in the N-terminal domain (Cys36) and the third extracellular loop (Cys288) neither significantly affected receptor surface expression nor completely abolished receptor function. Importantly, contrary to several previous reports, we demonstrated directly that instead of forming a disulfide bond, the N-terminal cysteine (Cys36) and the third extracellular loop cysteine (Cys288) contain free SH groups. The cysteine residues (Cys36 and Cys288), rather than forming a disulfide bond, may be important per se. We propose that CCR6 forms only a disulfide bond between the first (Cys118) and second (Cys197) extracellular loops, which confines a helical bundle together with the N-terminus adjacent to the third extracellular loop, creating the structural organization critical for ligand binding and therefore for receptor signaling.