title: The role of alanine 163 in solute permeability of Leishmania major aquaglyceroporin LmAQP1.
abstract: Leishmania major aquaglyceroporin LmAQP1 allows adventitious passage of antimonite, an activated form of the drug Pentostam, which is used as the first line treatment for leishmaniasis. The extracellular C-loop of an aquaglyceroporin confers substrate specificity. Alteration of Glu125 to serine in the Plasmodium falciparum aquaglyceroporin PfAQP has been shown to selectively affect water but not glycerol permeability. The C-loop of LmAQP1 is twelve residues longer than PfAQP, and Ala163 is at an equivalent position as Glu125 of PfAQP. The role of Ala163 in LmAQP1 solute permeability was investigated. Alteration of Ala163 to serine or threonine did not significantly affect conduction of solutes. However, alteration to aspartate, glutamate, and glutamine blocked passage of water, glycerol, and other organic solutes. While LmAQP1 is a mercurial insensitive water channel, mutation of the adjacent threonine (Thr164) to cysteine led to inhibition of water passage by Hg(2+). This inhibition could be reversed upon addition of β-mercaptoethanol. These data suggest that, unlike Glu125 (PfAQP), Ala163 is not involved in stabilization of the C-loop and selective solute permeability. Ala163 is located near the pore mouth of the channel, and replacement of Ala163 by bulkier residue sterically hinders the passage of solutes. Alteration of Ala163 to serine or threonine affected metalloid uptake in the order, wild-type>A163S>A163T. Metalloid conduction was near completely blocked when Ala163 was mutagenized to aspartate, glutamate, or glutamine. Mutations such as A163S and A163T that reduced the permeability to antimonite, without a significant loss in water or solute conductivity raises the possibility that, subtle changes in the side chain of the amino acid residue in position 163 of LmAQP1 may play a role in drug resistance.
authors.affiliation: Department of Molecular Microbiology and Infectious Diseases, Florida International University, Herbert Wertheim College of Medicine, 11200 SW 8th Street, Miami, FL 33199, USA. rmukhop@fiu.edu
authors.forename: Rita
authors.initials: R
authors.lastname: Mukhopadhyay
authors.forename: Goutam
authors.initials: G
authors.lastname: Mandal
authors.forename: Venkata Subba Rao
authors.initials: VS
authors.lastname: Atluri
authors.forename: Katherine
authors.initials: K
authors.lastname: Figarella
authors.forename: Nestor L
authors.initials: NL
authors.lastname: Uzcategui
authors.forename: Yao
authors.initials: Y
authors.lastname: Zhou
authors.forename: Eric
authors.initials: E
authors.lastname: Beitz
authors.forename: A Abdul
authors.initials: AA
authors.lastname: Ajees
authors.forename: Hiranmoy
authors.initials: H
authors.lastname: Bhattacharjee
mesh_terms: D000409:Alanine / Q000235:genetics*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000965:Antimony / Q000378:metabolism*; D051397:Aquaglyceroporins / Q000235:genetics* / Q000378:metabolism*; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D018320:Leishmania major / Q000235:genetics* / Q000378:metabolism*; D008623:Mercaptoethanol / Q000378:metabolism; D008628:Mercury / Q000378:metabolism; D058955:Metalloids / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D009930:Organic Chemicals / Q000378:metabolism; D017434:Protein Structure, Tertiary; D019163:Reducing Agents / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D051397:Aquaglyceroporins; D004791:Enzyme Inhibitors; D058955:Metalloids; D050505:Mutant Proteins; D009930:Organic Chemicals; D019163:Reducing Agents; D014867:Water; C061374:antimonite; D008623:Mercaptoethanol; D000965:Antimony; D008628:Mercury; D000409:Alanine; D005990:Glycerol