Bioluminescence of (R)-Cypridina Luciferin with Cypridina Luciferase

Cypridina luciferin (CypL) is a marine natural product that functions as the luminous substrate for the enzyme Cypridina luciferase (CypLase). CypL has two enantiomers, (R)- and (S)-CypL, due to its one chiral center at the sec-butyl moiety. Previous studies reported that (S)-CypL or racemic CypL with CypLase produced light, but the luminescence of (R)-CypL with CypLase has not been investigated. Here, we examined the luminescence of (R)-CypL, which had undergone chiral separation from the enantiomeric mixture, with a recombinant CypLase. Our luminescence measurements demonstrated that (R)-CypL with CypLase produced light, indicating that (R)-CypL must be considered as the luminous substrate for CypLase, as in the case of (S)-CypL, rather than a competitive inhibitor for CypLase. Additionally, we found that the maximum luminescence intensity from the reaction of (R)-CypL with CypLase was approximately 10 fold lower than that of (S)-CypL with CypLase, but our kinetic analysis of CypLase showed that the Km value of CypLase for (R)-CypL was approximately 3 fold lower than that for (S)-CypL. Furthermore, the chiral high-performance liquid chromatography (HPLC) analysis of the reaction mixture of racemic CypL with CypLase showed that (R)-CypL was consumed more slowly than (S)-CypL. These results indicate that the turnover rate of CypLase for (R)-CypL was lower than that for (S)-CypL, which caused the less efficient luminescence of (R)-CypL with CypLase.

Potential use of Cypridina luciferin for quantifying alpha 1-acid glycoprotein in human serum

Alpha 1-acid glycoprotein (AGP) is an acute phase protein in mammals, including humans. The amount of AGP in human serum varies in response to certain diseases; thus, many efforts have been made to develop methods for quantifying human AGP. We recently discovered that luminescence occurs merely by mixing Cypridina luciferin with human AGP under human serum-free neutral or basic buffer conditions. In this study, we tested an application of Cypridina luciferin for quantifying AGP contained in human serum. Our luminescence spectrum measurements of Cypridina luciferin with human serum samples showed that the maximum emission wavelength with human serum (480 nm) differed from that with human AGP (464 nm) due to the abundant presence of endogenous human serum albumin (HSA). Furthermore, the luminescence intensities of Cypridina luciferin with human AGP in HSA-depleted human serum were consistent with those in a human serum-free basic buffer, but those in human serum were not. These results indicated that depletion of HSA in human serum was required to use Cypridina luciferin for quantifying AGP in human serum. Additionally, we found that the luminescence intensity of Cypridina luciferin with bovine AGP was approximately tenfold lower than that with human AGP.

Multiple Cypridina Luciferase Genes in the Genome of Individual Ostracods, Vargula hilgendorfii (Cypridina hilgendorfii)

The genomic structure of the Cypridina luciferase gene in Vargula hilgendorfii (formerly Cypridina hilgendorfii) was determined with three λ phage clones (λ34, λ45, and λ61). The luciferase genes in clones λ34 and λ61 consisted of 13 exons and 12 introns, and clone λ45 only contained exons 1-5. The splicing sites of the luciferase genes in λ34 and λ61 were conserved completely with the consensus sequence. The translated luciferases had 555 amino acid residues, which were over 98.6% identical to those of cDNA clones as previously reported. In contrast, each intron in clones λ34, λ45, and λ61 varied significantly in length. To explain the variation of intron length among the three V. hilgendorfii luciferase genes, genomic DNA was isolated from a single V. hilgendorfii specimen and the regions from exon 1-3 of the luciferase gene were amplified by polymerase chain reaction (PCR). PCR products with various lengths were detected and were confirmed as the luciferase gene fragments by Southern blot analysis. Furthermore, DNA sequence analysis indicated that at least seven luciferase gene groups might be present in the genome of a single specimen. Thus, multiple Cypridina luciferase genes exist in the genome of a single V. hilgendorfii specimen.

Luminescence of Cypridina Luciferin in the Presence of Human Plasma Alpha 1-Acid Glycoprotein

The enzyme Cypridina luciferase (CLase) enables Cypridina luciferin to emit light efficiently through an oxidation reaction. The catalytic mechanism on the substrate of CLase has been studied, but the details remain to be clarified. Here, we examined the luminescence of Cypridina luciferin in the presence of several proteins with drug-binding ability. Luminescence measurements showed that the mixture of human plasma alpha 1-acid glycoprotein (hAGP) and Cypridina luciferin produced light. The total value of the luminescence intensity over 60 s was over 12.6-fold higher than those in the presence of ovalbumin, human serum albumin, or bovine serum albumin. In the presence of heat-treated hAGP, the luminescence intensity of Cypridina luciferin was lower than in the presence of intact hAGP. Chlorpromazine, which binds to hAGP, showed an inhibitory effect on the luminescence of Cypridina luciferin, both in the presence of hAGP and a recombinant CLase. Furthermore, BlastP analysis showed that hAGP had partial amino acid sequence similarity to known CLases in the region including amino acid residues involved in the drug-binding ability of hAGP. These findings indicate enzymological similarity between hAGP and CLase and provide insights into both the enzymological understanding of CLase and development of a luminescence detection method for hAGP.