High impact information on Es22

• Organophosphorous compounds, which are potent inhibitors of egasyn-esterase activity, caused a rapid dissociation of the high molecular weight egasyn-microsomal beta-glucuronidase complex when administered in vivo or when added in vitro to microsomal suspensions [1].
• These experiments implicate the egasyn-esterase active site in attachment of microsomal beta-glucuronidase to egasyn by a novel mechanism that, in turn, compartmentalizes beta-glucuronidase within the endoplasmic reticulum [1].
• The hydrophilic nature of both the complex and free egasyn was confirmed by phase separation experiments with the detergent Triton X-114 [2].
• The results indicate that the relative availability of egasyn determines the balance between glucuronidase incorporation into membranes and that into lysosomes [3].
• By means of a recently developed radioimmunoassay for egasyn, the relationship between microsomal glucuronidase levels and egasyn levels has been examined in various adult tissues, during postnatal development in liver, and after androgen induction of glucuronidase in kidney [3].

Biological context of Es22

• PCR primers were based upon: (1) partial amino acid sequences derived from egasyn peptides and (2) a conserved active site region shared by carboxylesterases [4].
• The features of the deduced amino acid sequence of the egasyn cDNA are compared with previously characterized carboxylesterases and with other lumenal ER proteins [4].
• Genetic mapping confirmed the location of an egasyn cDNA fragment in cluster 1 of the esterase region on chromosome 8 [4].
• Egasyn (esterase-22), a member of the nonspecific carboxylesterase multigene family (E.C. 3.1.1.1), is the endoplasmic reticulum (ER)-targeting protein of beta-glucuronidase [4].
• Transfection of COS cells with the 2022-bp cDNA resulted in the expression of esterase activity, which comigrated on native gels with liver esterase-22 [4].

Anatomical context of Es22

• Recent experiments have demonstrated that egasyn not only sequesters beta-glucuronidase in microsomes by forming high molecular weight complexes with beta-glucuronidase, but also has carboxyl esterase activity [5].
• Glucuronidase present in lysosomes of mouse liver occurs as the free tetramer, whereas glucuronidase present in endoplasmic reticulum occurs in macromolecular complexes containing one to four molecules of the protein egasyn [6].
• Mouse egasyn cDNA was inserted into expression vector pCDpoly and transfected into mammalian cell lines [7].
• The esterases were, like egasyn and microsomal beta-glucuronidase, concentrated in the microsomal subcellular fraction [8].
• A significant portion of murine hepatocyte beta-glucuronidase is maintained within the endoplasmic reticulum (ER) by complex formation with the esterase active site of the protein egasyn [9].

Associations of Es22 with chemical compounds

• We have now purfied egasyn by releasing it from antiglucuronidase immunoprecipitates of M forms under relatively mild conditions, such as treatment with deoxycholate or heating at 50 degrees [6].
• Most of the antigenic sites of egasyn in homogenates of normal liver are masked after extraction with Triton X-100 and only become immunoreactive after exposure to deoxycholate [6].
• Isolated egasyn is a glycoprotein of molecular weight about 64,000 and is not unusually hydrophobic in amino acid composition [6].
• A procedure for the radioimmunoassay of egasyn was developed utilizing egasyn labeled with iodine 125 [6].
• Taken together, these results suggest that (a) the egasyn-glucuronidase system may use a novel mechanism related to that of serine proteinases and their inhibitors in complex formation and in subsequent localization of glucuronidase within the ER and that (b) a possible function of ER glucuronidase is to modulate the esterase activity of egasyn [9].

Physical interactions of Es22

• An accessory protein identical to mouse egasyn is complexed with rat microsomal beta-glucuronidase and is identical to rat esterase-3 [10].

Other interactions of Es22

• Several phenotypes corresponded in relative mobility and relative isoelectric point among inbred strains to that recently reported for esterase-22 by Eisenhardt and von Deimling [(1982). Comp. Biochem. Physiol. 73B:719] [5].
• Combined experiments measuring susceptibility to neuraminidase and to endoglycosidase H and specific binding to Ricinus communis lectin-agarose columns showed that the alterations in isoelectric point were associated with a decrease in complex oligosaccharides of lysosomal beta-glucuronidase in egasyn-positive mice [11].
• This carboxylesterase consisted of 554 amino acid residues, and exhibited 43% and 42% similarities to the known mouse esterases Es-22 and pEs-N, respectively [12].

Analytical, diagnostic and therapeutic context of Es22

• The amino acid sequence deduced from the PCR product matched that obtained from egasyn protein [4].
• We have found several new phenotypes of egasyn-esterase after electrophoresis and isoelectric focusing of liver homogenates and purified egasyn of inbred and wild mouse strains [5].
• Castration of mice lead to the appearance of free and complexed egasyn forms in the proximal epididymis [13].

References