Spermidine is a polyamine formed from putrescine. It is found in almost all tissues in association with nucleic acids. It is found as a cation at all pH values, and is thought to help stabilize some membranes and nucleic acid structures. It is a precursor of spermine. Inhibits some lipases CarbLipBact_2 or moderately activates others
Spermidine ligand of proteins in family: CarbLipBact_2
Stucture
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1 structure: 4FBL: LipS and LipT, two metagenome-derived lipolytic enzymes increase the diversity of known lipase and esterase families 1. This is LipS
Comparative Gene Identification-58 (CGI-58) is an alpha/beta hydrolase-type protein that regulates lipid homeostasis and signaling in eukaryotes by interacting with and stimulating the activity of several different types of proteins, including a lipase in mammalian cells and a peroxisomal ABC transporter (PXA1) in plant cells. Here we show that plant CGI-58 also interacts with spermidine synthase 1 (SPDS1), an enzyme that plays a central role in polyamine metabolism by converting putrescine into spermidine. Analysis of polyamine contents in Arabidopsis thaliana plants revealed that spermidine levels were significantly reduced, and putrescine increased, in both cgi-58 and cgi-58/pxa1 mutant plants, relative to pxa1 mutant or wild-type plants. Evaluation of polyamine-related gene expression levels, however, revealed similar increases in transcript abundance in all mutants, including cgi-58, pxa1, and cgi-58/pxa1, in comparison to wild type. Taken together, the data support a model whereby CGI-58 and PXA1 contribute to the regulation of polyamine metabolism at the transcriptional level, perhaps through a shared lipid-signaling pathway, and that CGI-58 also acts independently of PXA1 to increase spermidine content at a post-transcriptional level, possibly through protein-protein interaction with SPDS1.
Triacylglycerol lipases (EC 3.1.1.3) catalyze both hydrolysis and synthesis reactions with a broad spectrum of substrates rendering them especially suitable for many biotechnological applications. Most lipases used today originate from mesophilic organisms and are susceptible to thermal denaturation whereas only few possess high thermotolerance. Here, we report on the identification and characterization of two novel thermostable bacterial lipases identified by functional metagenomic screenings. Metagenomic libraries were constructed from enrichment cultures maintained at 65 to 75 degrees C and screened resulting in the identification of initially 10 clones with lipolytic activities. Subsequently, two ORFs were identified encoding lipases, LipS and LipT. Comparative sequence analyses suggested that both enzymes are members of novel lipase families. LipS is a 30.2 kDa protein and revealed a half-life of 48 h at 70 degrees C. The lipT gene encoded for a multimeric enzyme with a half-life of 3 h at 70 degrees C. LipS had an optimum temperature at 70 degrees C and LipT at 75 degrees C. Both enzymes catalyzed hydrolysis of long-chain (C(12) and C(14)) fatty acid esters and additionally hydrolyzed a number of industry-relevant substrates. LipS was highly specific for (R)-ibuprofen-phenyl ester with an enantiomeric excess (ee) of 99%. Furthermore, LipS was able to synthesize 1-propyl laurate and 1-tetradecyl myristate at 70 degrees C with rates similar to those of the lipase CalB from Candida antarctica. LipS represents the first example of a thermostable metagenome-derived lipase with significant synthesis activities. Its X-ray structure was solved with a resolution of 1.99 A revealing an unusually compact lid structure.
