title: Lactate dehydrogenase A as a highly abundant eye lens protein in platypus (Ornithorhynchus anatinus): upsilon (upsilon)-crystallin.
abstract: Vertebrate eye lenses mostly contain two abundant types of proteins, the alpha-crystallins and the beta/gamma-crystallins. In addition, certain housekeeping enzymes are highly expressed as crystallins in various taxa. We now observed an unusual approximately 41-kd protein that makes up 16% to 18% of the total protein in the platypus eye lens. Its cDNA sequence was determined, which identified the protein as muscle-type lactate dehydrogenase A (LDH-A). It is the first observation of LDH-A as a crystallin, and we designate it upsilon (upsilon)-crystallin. Interestingly, the related heart-type LDH-B occurs as an abundant lens protein, known as epsilon-crystallin, in many birds and crocodiles. Thus, two members of the ldh gene family have independently been recruited as crystallins in different higher vertebrate lineages, suggesting that they are particularly suited for this purpose in terms of gene regulatory or protein structural properties. To establish whether platypus LDH-A/upsilon-crystallin has been under different selective constraints as compared with other vertebrate LDH-A sequences, we reconstructed the vertebrate ldh-a gene phylogeny. No conspicuous rate deviations or amino acid replacements were observed.
authors.affiliation: Department of Biochemistry, University of Nijmegen, Nijmegen, The Netherlands.
authors.forename: Teun
authors.initials: T
authors.lastname: van Rheede
authors.forename: Reinout
authors.initials: R
authors.lastname: Amons
authors.forename: Niall
authors.initials: N
authors.lastname: Stewart
authors.forename: Wilfried W
authors.initials: WW
authors.lastname: de Jong
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003459:Crystallins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D004591:Electrophoresis, Polyacrylamide Gel; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000080864:Lactate Dehydrogenase 5; D008297:Male; D008969:Molecular Sequence Data; D010987:Platypus; D017386:Sequence Homology, Amino Acid
chemical_list: D003459:Crystallins; D017931:DNA Primers; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase; D000080864:Lactate Dehydrogenase 5