title: An unusual halotolerant alpha-type carbonic anhydrase from the alga Dunaliella salina functionally expressed in Escherichia coli.
abstract: A 60-kDa, salt-inducible, internally duplicated alpha-type carbonic anhydrase (Dca) is associated with the plasma membrane of the extremely salt-tolerant, unicellular, green alga Dunaliella salina. Unlike other carbonic anhydrases, Dca remains active over a very broad range of salinities (0-4M NaCl), thus representing a novel type of extremely halotolerant enzyme. To elucidate the structural principles of halotolerance, structure-function investigations of Dca have been initiated. Such studies require considerable amounts of the enzyme, and hence, large-scale algal cultivation. Furthermore, the purified enzyme is often contaminated with other, co-purifying algal carbonic anhydrases. Expression in heterologous systems offers a means to produce, and subsequently purify, sufficiently large amounts of Dca required for activity and structural studies. Attempts to over-express Dca in the Escherichia coli BL21(DE3)pLysS strain, after optimizing various expression parameters, produced soluble, but weakly active protein, composed of fully reduced and variably -S-S- cross-linked chains (each of the Dca repeats contains a pair of cysteine residues, presumably forming a disulfide bond). However, when the E. coli Origami B(DE3)pLysS strain was used as a host, a functionally active enzyme with proper disulfide bonds was formed in good yield. Affinity-purified recombinant Dca resembled the native enzyme from D. salina in activity and salt tolerance. Hence, this expression system offers a means of pursuing detailed studies of this extraordinary protein using biochemical, biophysical, and crystallographic approaches.
authors.affiliation: Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Lakshmanane
authors.initials: L
authors.lastname: Premkumar
authors.forename: Umesh K
authors.initials: UK
authors.lastname: Bageshwar
authors.forename: Irena
authors.initials: I
authors.lastname: Gokhman
authors.forename: Ada
authors.initials: A
authors.lastname: Zamir
authors.forename: Joel L
authors.initials: JL
authors.lastname: Sussman
mesh_terms: D000595:Amino Acid Sequence; D002256:Carbonic Anhydrases / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D004220:Disulfides; D004926:Escherichia coli / Q000235:genetics*; D056890:Eukaryota / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012492:Salts / Q000494:pharmacology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D004220:Disulfides; D011994:Recombinant Proteins; D012492:Salts; D002256:Carbonic Anhydrases