title: Characterization of protein transacetylase from human placenta as a signaling molecule calreticulin using polyphenolic peracetates as the acetyl group donors.
abstract: We have earlier shown that a unique membrane-bound enzyme mediates the transfer of acetyl group(s) from polyphenolic peracetates (PA) to functional proteins, which was termed acetoxy drug: protein transacetylase (TAase) because it acted upon several classes of PA. Here, we report the purification of TAase from human placental microsomes to homogeneity with molecular mass of 60 kDa, exhibiting varying degrees of specificity to several classes of PA confirming the structure-activity relationship for the microsome-bound TAase. The TAase catalyzed protein acetylation by a model acetoxy drug, 7,8-diacetoxy-4-methyl coumarin (DAMC) was established by the demonstration of immunoreactivity of the acetylated target protein with anti-acetyl lysine antibody. TAase activity was severely inhibited in calcium-aggregated microsomes as well as when Ca2+ was added to purified TAase, suggesting that TAase could be a calcium binding protein. Furthermore, the N-terminal sequence analysis of purified TAase (EPAVYFKEQFLD) using Swiss Prot Database perfectly matched with calreticulin (CRT), a major microsomal calcium binding protein of the endoplasmic reticulum (ER). The identity of TAase with CRT was substantiated by the observation that the purified TAase avidly reacted with commercially available antibody raised against the C-terminus of human CRT (13 residues peptide, DEEDATGQAKDEL). Purified TAase also showed Ca2+ binding and acted as a substrate for phosphorylation catalyzed by protein kinase C (PKC), which are hallmark characteristics of CRT. Further, purified placental CRT as well as the commercially procured pure CRT yielded significant TAase catalytic activity and were also found effective in mediating the acetylation of the target protein NADPH cytochrome P-450 reductase by DAMC as detected by Western blot using anti-acetyl lysine antibody. These observations for the first time convincingly attribute the transacetylase function to CRT. Hence, this transacetylase function of CRT is designated calreticulin transacetylase (CRTAase). We envisage that CRTAase plays an important role in protein modification by way of acetylation independent of Acetyl CoA.
authors.affiliation: Biochemistry Department, V.P.Chest Institute, University of Delhi, Delhi-110007, India.
authors.lastname: Seema
authors.forename: Ranju
authors.initials: R
authors.lastname: Kumari
authors.forename: Garima
authors.initials: G
authors.lastname: Gupta
authors.forename: Daman
authors.initials: D
authors.lastname: Saluja
authors.forename: Ajit
authors.initials: A
authors.lastname: Kumar
authors.forename: Sanjay
authors.initials: S
authors.lastname: Goel
authors.forename: Yogesh K
authors.initials: YK
authors.lastname: Tyagi
authors.forename: Ruchika
authors.initials: R
authors.lastname: Gulati
authors.forename: Anjali
authors.initials: A
authors.lastname: Vinocha
authors.forename: Kambadoor
authors.initials: K
authors.lastname: Muralidhar
authors.forename: Bilikere S
authors.initials: BS
authors.lastname: Dwarakanth
authors.forename: Ramesh C
authors.initials: RC
authors.lastname: Rastogi
authors.forename: Virinder S
authors.initials: VS
authors.lastname: Parmar
authors.forename: Shamkant A
authors.initials: SA
authors.lastname: Patkar
authors.forename: Hanumantharao G
authors.initials: HG
authors.lastname: Raj
mesh_terms: D000085:Acetates / Q000737:chemistry*; D000123:Acetyltransferases / Q000737:chemistry / Q000502:physiology*; D002118:Calcium / Q000737:chemistry; D037282:Calreticulin / Q000378:metabolism*; D003374:Coumarins / Q000737:chemistry; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005419:Flavonoids / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D010636:Phenols / Q000737:chemistry*; D010920:Placenta / Q000378:metabolism*; D059808:Polyphenols; D011485:Protein Binding; D011487:Protein Conformation; D011493:Protein Kinase C / Q000378:metabolism; D017434:Protein Structure, Tertiary; D015398:Signal Transduction
chemical_list: C114369:7,8-diacetoxy-4-methylcoumarin; D000085:Acetates; D037282:Calreticulin; D003374:Coumarins; D005419:Flavonoids; D010636:Phenols; D059808:Polyphenols; D000123:Acetyltransferases; D011493:Protein Kinase C; D002118:Calcium