Daniel C.-H. Lin

Bio: Daniel C.-H. Lin is an academic researcher from Amgen. The author has contributed to research in topics: Agonist & Free fatty acid receptor 1. The author has an hindex of 22, co-authored 29 publications receiving 4053 citations. Previous affiliations of Daniel C.-H. Lin include Massachusetts Institute of Technology.

Citric acid cycle intermediates as ligands for orphan G-protein-coupled receptors

Abstract: The citric acid cycle is central to the regulation of energy homeostasis and cell metabolism. Mutations in enzymes that catalyse steps in the citric acid cycle result in human diseases with various clinical presentations. The intermediates of the citric acid cycle are present at micromolar concentration in blood and are regulated by respiration, metabolism and renal reabsorption/extrusion. Here we show that GPR91 (ref. 3), a previously orphan G-protein-coupled receptor (GPCR), functions as a receptor for the citric acid cycle intermediate succinate. We also report that GPR99 (ref. 4), a close relative of GPR91, responds to alpha-ketoglutarate, another intermediate in the citric acid cycle. Thus by acting as ligands for GPCRs, succinate and alpha-ketoglutarate are found to have unexpected signalling functions beyond their traditional roles. Furthermore, we show that succinate increases blood pressure in animals. The succinate-induced hypertensive effect involves the renin-angiotensin system and is abolished in GPR91-deficient mice. Our results indicate a possible role for GPR91 in renovascular hypertension, a disease closely linked to atherosclerosis, diabetes and renal failure.

Characterization of a prokaryotic SMC protein involved in chromosome partitioning

Abstract: Efficient partitioning of chromosomes into dividing cells is important for cell survival. In Escherichia coli and Bacillus subtilis, chromosomes partition to daughter cells with high fidelity (Hiraga et al. 1989; Ireton et al. 1994). Although proteins, sites, and mechanisms involved in physical separation (decatenation) of bacterial chromosomes have been characterized, much less is known about the mechanisms governing efficient partitioning to daughter cells (for review, see Hiraga 1992; Wake and Errington 1995). Recent work has shown that the chromosomal region around the origin of replication (oriC) is in a defined orientation for most of the bacterial (B. subtilis and E. coli) cell cycle and that newly replicated oriC regions are rapidly separated from each other (Glaser et al. 1997; Gordon et al. 1997; Lin et al. 1997; Webb et al. 1997). The origin regions are found toward the poles of the highly condensed nucleoid body, oriented toward the ends of the cell. The rapid separation and localization of oriC regions indicate the function of a mitotic-like apparatus in prokaryotes (Glaser et al. 1997; Gordon et al. 1997; Lin et al. 1997; Webb et al. 1997). Cellular proteins contributing to efficient chromosome partitioning have recently been characterized. Spo0J from B. subtilis and ParB from Caulobacter crescentus are required for efficient chromosome partitioning and are similar to a family of plasmid-encoded proteins required for plasmid partitioning in E. coli (e.g., ParB for P1 and SopB for F). ParB of C. crescentus is essential for growth, and overexpression causes a defect in chromosome partitioning (Mohl and Gober 1997). Deletion of spo0J in B. subtilis causes an ∼100-fold increase in the number of anucleate cells, resulting in accumulation of 1%–2% anucleate cells in a growing culture (Ireton et al. 1994). Spo0J binds to at least eight sites located in the origin proximal 20% of the chromosome (Lin and Grossman 1998). Spo0J is found in the cell in single discrete foci located near the poles of the nucleoid body (Glaser et al. 1997; Lin et al. 1997), in a pattern similar to that observed for the region around the origin of replication (Lewis and Errington 1997; Webb et al. 1997). Visualization of the foci of Spo0J by immunofluorescence microscopy or by use of a Spo0J–green fluorescent protein (GFP) fusion indicates the assembly of a large nucleoprotein complex containing Spo0J. The function of Spo0J and other proteins of this family is still unknown, though they are thought to be involved in pairing and/or positioning sister chromosomes (Nordstrom and Austin 1989; Niki and Hiraga 1997; Lin and Grossman 1998). The muk genes of E. coli were identified in an elegant screen for mutants that produce anucleate cells (Hiraga et al. 1989). The mukB gene product has features of a myosin-like motor protein and is involved in chromosome condensation and/or movement [(Niki et al. 1991; Hiraga 1992; Wake and Errington 1995; Hu et al. 1996), and references therein]. mukE and mukF, which are in an operon with mukB, are also required for efficient partitioning and their products are thought to interact with MukB (Yamanaka et al. 1996). Of the ∼12 bacterial genomes that have been sequenced, mukB, mukE, and mukF are found only in E. coli and Haemophilus influenzae. B. subtilis, along with many other bacterial species (but not E. coli or H. influenzae), contains a homolog of the eukaryotic Smc (structural maintenance of chromosomes) proteins (Oguro et al. 1996). Several eukaryotes have multiple smc genes, and eukaryotic Smc proteins play a role in chromosome condensation, pairing, and/or segregation (for review, see Hirano et al. 1995; Koshland and Strunnikov 1996; Heck 1997). For example, mutations in the SMC genes of Saccharomyces cerevisiae cause defects in chromosome condensation, segregation, and sister chromatid cohesion (Guacci et al. 1997; Michaelis et al. 1997). DNA condensation by the 13S condensin of Xenopus laevis requires two Smc proteins, XCAP-C and XCAP-E (Hirano et al. 1997). Dosage compensation in Caenorhabditis elegans involves specific interaction of an Smc homolog, Dpy-27, and other proteins, with the X chromosome (Chuang et al. 1994, 1996). Although the precise biochemical function of the Smc proteins is not known, recent work has shown that Smc proteins, or complexes containing Smc proteins, can affect DNA topology in vitro (Kimura and Hirano 1997; Sutani and Yanagida 1997). The smc gene of B. subtilis encodes a 135-kD protein that is homologous to eukaryotic Smc proteins (Oguro et al. 1996). B. subtilis Smc is ∼24% identical and ∼46% similar to SMC1 and SMC2 (S. cerevisiae), XCAP-C and XCAP-E (X. laevis), Dpy-27 (C. elegans), and Cut3 and Cut14 (Schizosaccaromyces pombe). It contains all of the domains associated with the Smc family; an amino-terminal NTP-binding domain, two internal coiled–coil regions separated by a hinge, and the carboxy-terminal signature “DA-box” motif (Hirano et al. 1995; Koshland and Strunnikov 1996). Whereas the existence of Smc proteins in eukaryotes is well documented, their prevalence in bacteria and archaebacteria is only beginning to be appreciated. A search of GenBank and individual sequence databases (both completed and in progress) revealed that at least 11 bacteria and 2 archaebacteria contain genes encoding homologs of Smc. In addition to B. subtilis, the list includes Streptococcus pyogenes, Streptococcus pneumoniae, Mycobacterium tuberculosis, several Mycoplasma species (M. genitalium, M. pneumoniae, and M. hyorhinis), Borrelia burgdorferi, Treponema pallidum, Synechocystis sp., Neisseria gonorrhoeae, and the archaebacteria Methanococcus jannaschii and Archaeoglobus fulgidus. We report the characterization of the B. subtilis smc gene. Null mutations in smc caused a conditional lethal phenotype, alterations in nucleoid appearance, a defect in chromosome partitioning, and a synthetic phenotype with a null mutation in spo0J. These findings indicate that the function of Smc proteins is highly conserved.

Complete genome sequence of the model actinomycete Streptomyces coelicolor A3(2)

Abstract: Streptomyces coelicolor is a representative of the group of soil-dwelling, filamentous bacteria responsible for producing most natural antibiotics used in human and veterinary medicine. Here we report the 8,667,507 base pair linear chromosome of this organism, containing the largest number of genes so far discovered in a bacterium. The 7,825 predicted genes include more than 20 clusters coding for known or predicted secondary metabolites. The genome contains an unprecedented proportion of regulatory genes, predominantly those likely to be involved in responses to external stimuli and stresses, and many duplicated gene sets that may represent 'tissue-specific' isoforms operating in different phases of colonial development, a unique situation for a bacterium. An ancient synteny was revealed between the central 'core' of the chromosome and the whole chromosome of pathogens Mycobacterium tuberculosis and Corynebacterium diphtheriae. The genome sequence will greatly increase our understanding of microbial life in the soil as well as aiding the generation of new drug candidates by genetic engineering.

Metabolite profiles and the risk of developing diabetes

Abstract: Emerging technologies allow the high-throughput profiling of metabolic status from a blood specimen (metabolomics) We investigated whether metabolite profiles could predict the development of diabetes Among 2,422 normoglycemic individuals followed for 12 years, 201 developed diabetes Amino acids, amines and other polar metabolites were profiled in baseline specimens by liquid chromatography-tandem mass spectrometry (LC-MS) Cases and controls were matched for age, body mass index and fasting glucose Five branched-chain and aromatic amino acids had highly significant associations with future diabetes: isoleucine, leucine, valine, tyrosine and phenylalanine A combination of three amino acids predicted future diabetes (with a more than fivefold higher risk for individuals in top quartile) The results were replicated in an independent, prospective cohort These findings underscore the potential key role of amino acid metabolism early in the pathogenesis of diabetes and suggest that amino acid profiles could aid in diabetes risk assessment