C‐terminal CTII motif of 2′,3′‐cyclic nucleotide 3′‐phosphodiesterase undergoes carboxylmethylation

Abstract

Eukaryotic proteins with a carboxyl-terminal CaaX motif are modified by isoprenylation and subsequently processed by proteolysis of the three terminal amino acids and carboxylmethylation of the exposed cysteine residue. The myelination-associated 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) has a C-terminal CTII sequence and is isoprenylated; however, no examples of subsequent processing exist when threonine, a polar residue, is located adjacent to the cysteine. Here we show that CNP is capable of being carboxylmethylated in both insect cells and glioma cells. This processing is dependent upon isoprenylation of the cysteine and can be inhibited with the isoprenylated cysteine derivative, N-acetyl-S-farnesyl-L-cysteine. Although the role of the methyl group at the C-terminus of other isoprenylated proteins is not fully understood, modulation of signal transduction pathways is strongly indicated. This modification of CNP may similarly regulate cell biological processes in myelinogenesis.

Dual implication of 2',3'-cyclic nucleotide 3' phosphodiesterase as major autoantigen and C3 complement-binding protein in the pathogenesis of multiple sclerosis.

“…3, a -c , is representative, illustrating results for one MS patient using CSF (diluted 1:10) and serum (diluted 1:2,000 or 1:5,000) and showing an intense reaction directed almost exclusively against the CNPI isoform. This result was surprising, because the entire primary sequence of CNPI is included within CNPII, and it suggests that the epitope recognized is a posttranslational modification unique to the blocked amino terminus of CNPI (13), or lipid modifications including palmitoylation and isoprenylation unique to one CNP isoform (16,17), or other modifications still unidentified.…”

“…CNPI (46 kD) and CNPII (48 kD) are derived by alternative splicing from a single gene, and are identical except for an additional 20 amino acids at the amino terminus of CNPII (15). Both CNPII and CNPI are highly modified posttranslationally and differentially, including serine/ threonine phosphorylation, palmitoylation, and isoprenylation, and are heterogenous in size and charge (11,12,16,17). The antibody response is directed against CNPI, whereas both isoforms, but particularly CNPII, bind avidly to C3, a pivotal protein of the complement system highly implicated in MS (18) and its experimental models (19).…”

A Comparative Study of 2′,3′‐Cyclic‐Nucleotide 3′‐Phosphodiesterase in Vertebrates: cDNA Cloning and Amino Acid Sequences for Chicken and Bullfrog Enzymes

“…CNP activity hydrolyzing 2 ',3 '-cyclic nucleotides seems to be irrelevant to the above sequence. Mammalian CNP undergoes isoprenylation and then carboxymethylation at the carboxyl-terminal CTII and becomes membrane-bound (Braun et al, 1991;Cox et al, 1994;De Angelis and Braun, 1994). The isoprenylation sequence is conserved also in nonmammalian vertebrates (CTIN in chick and CHIM in bullfrog; Fig.…”

2′,3′ cyclic nucleotide 3′ phosphodiesterase 1 functional isoform antagonizes HIV-1 particle assembly

“…CNP1 proteins, translated from CNP1 mRNA or alternatively from the second start codon of CNP2 mRNA ( O’Neill et al, 1997 ), predominantly localize on the plasma membrane ( Braun et al, 1991 ). The C-terminal CTII motif prenylation regulates the plasma membrane localization of CNP1 ( Braun et al, 1991 ; Cox et al, 1994 ; Bifulco et al, 2002 ). The long isoform CNP2 proteins possess an additional N-terminal 20 amino acids (N20aa) proposed as a mitochondrial targeting sequence (MTS) ( Lee et al, 2006 ).…”