Metridia luciferase (MLuc)
Naturally secreted bioluminescent enzyme from the marine copepod Metridia longa with 24 kDa size and blue emission at 480 nm. Unique N-terminal signal peptide enables extracellular secretion from mammalian cells, permitting non-destructive reporter assays and real-time monitoring without cell lysis.
Origin: Metridia longa
Characteristics
219-amino acid polypeptide (23.9 kDa) contains a 17-residue N-terminal signal peptide directing natural secretion in mammalian expression systems. Uses coelenterazine as substrate to produce blue bioluminescence with peak emission at 480 nm. Secretion into culture medium occurs within 1 hour of medium replacement with continuous accumulation over time. No cytotoxicity observed in stably transfected CHO cells. Activity appears exclusively extracellular unlike firefly or Renilla luciferases which remain intracellular. Maintains enzymatic activity in culture medium for extended periods enabling longitudinal monitoring of the same cell populations.
Applications: Non-destructive reporter gene assays enabling live-cell monitoring and multiple sequential measurements on the same cells. Real-time detection of GPCR activity with agonist stimulation producing strong bioluminescent responses in culture medium. Ultra-high throughput screening applications where cell lysis is impractical or undesirable. cAMP-sensitive promoter monitoring for Gs-coupled and Gi-coupled receptor signaling. Kinetic studies of gene expression dynamics without sacrificing cells. Secretome analysis and protein trafficking studies leveraging natural extracellular localization.
Limitations: Blue emission at 480 nm provides poor tissue penetration depth for in vivo imaging compared to red-shifted luciferases. Requires coelenterazine substrate which has lower membrane permeability than D-luciferin and higher background autoluminescence than furimazine. Secretion-dependent signal necessitates medium sampling or supernatant transfer for detection in standard luminometers. Lower brightness compared to NanoLuc or enhanced firefly luciferases in equivalent expression systems. Natural secretion precludes use for intracellular protein localization or organelle targeting applications.