Title : Membrane topology and intracellular processing of
cyclin M2 (
CNNM2 )
Abstract :
- Recently, mutations in the cyclin M2 ( CNNM2 ) gene were identified to be causative for severe hypomagnesemia
- In kidney, CNNM2 is a basolaterally expressed protein with predominant expression in the distal convoluted tubule
- Transcellular magnesium ( Mg(2 +)) reabsorption in the distal convoluted tubule represents the final step before Mg(2 +) is excreted into the urine, thus fine-tuning its final excretion via a tightly regulated mechanism
- The present study aims to get insight in the structure of CNNM2 and to characterize its post-translational modifications
- Here, membrane topology studies using intramolecular epitopes and immunocytochemistry showed that CNNM2 has an extracellular N terminus and an intracellular C terminus
- This suggests that one of the predicted transmembrane regions might be re-entrant
- By homology modeling, we demonstrated that the loss-of-function mutation as found in patients disturbs the potential ATP binding by the intracellular cystathionine β-synthase domains
- In addition, the cellular processing pathway of CNNM2 was exposed in detail
- In the endoplasmic reticulum, the signal peptidase complex cleaves off a large N-terminal signal peptide of about 64 amino acids
- Mutagenesis screening showed that CNNM2 is glycosylated at residue Asn-112 , stabilizing CNNM2 on the plasma membrane
- Interestingly, co-immunoprecipitation studies evidenced that CNNM2a forms heterodimers with the smaller isoform CNNM2b
- These new findings on CNNM2 structure and processing may aid to elucidate the physiological role of CNNM2 in Mg(2 +) reabsorption in the kidney