- Email: [email protected]
crystallins
Thursday, Sep 24, 1992 Palazzo Dei Congressi/B
X ICER Abstracts 4
509
RECRUITMENT OF DETOXIFICATION ENZYMES AS LENS CRYSTALLINS CEPHALOPODS Tomarev. S.. Zfnovieva. R.. Piatmskv. J, National Eye Institute. IHDB. Bethesda, MD. USA
IN
The lenses of cephalopods and vertebrates are a classical example of convergent evolution. In contrast to vertebrates, the major crysrallins (S-crystallins) of the squid and octopus are a family of glutathione S-transferase (GST)-like proteins which are lensspecific and do not appear to possess enzymatic activity, The active GST was purified from the squid digestive gland and isolation of the corresponding gene is now in progress. In octopus there is another lens-specific crystallin (a-crystallin) which is related to aldehyde dehydrogenase (ALDH).n-crystallin is much less abundant in squid. Characterization ofa-crystallin cDNA clones of octopus and squid lens has shown that cephalopod&crystallins are more similar to cytoplasmic and mitochondrial ALDH than to the tumor-inducible and microsonal ALDH of vertebrates. Octopus and squida-crystallins were found to be more similar to each other than to the vertebrate Al.DHs or than the vertebrate ALMS are to each other. cDNA cloning and Northern blotting also provided information about cephalopod cytoskeletal proteins. A relatively abundant intermediate filament-like protein and less abundant Btubulin were found to be lens-specific in the octopus; by contrast, octopus a-tubulin was not lens-specific. Finally, structural and functional studies on 3 squid S-crystallin genes suggested that an overlapping AP-l/anti-oxidative responsive element n~ay be critical for expression of these genes and may have contributed to their recruitment as crystallins during evolution.
5
COMPARATIVE STAJRLITY . STUDIES . . . nstma Voorter. Department of Biochemistry, University Netherlands.
510 ON RNZYMJUCRYSTALLINS . Wrlfned de Jo ” g. of Nijmegen, Nijmegen, The
Lens proteins have, due to their longevity and environmental conditions, extraordinary requirements for structural stability. The finding that several house-keeping enzymes are recruited as eye lens proteins makes it possible to compare stability parameters from these enzym/crystallins in different tissues between species with abundant amounts of this enzyme in their lenses and those without it. We have compared the thermo- and urea-stability of LDH-B4, which is identical with t-crystallin, and abundantly present in lenses of several birds and reptiles. Measuring the thermostability of LDH-Et4 from different sources, the T, values (temperature at which 50% of the enzyme activity remains after a 20’ period) for LDH-B4 from duck heart, duck lens, chicken heart were found to be all around 76 “C, whereas pig heart LDH-B4 was less thermostable, having a T% value of 62 “C. A similar tendency was found with urea inactivation studies. Plotting the first order rate constants obtained from inactivation kinetic plots against the urea concentration it was clear that LDHB4 from pig heart was less stable in urea than the homologous enzymes from duck heart, chicken heart and duck lens. Therefore it is concluded that the avian heart LDH-B is apparently more stable than the homologous enzyme in mammals. This greater stability might make it suitable to function as “crystallin”, as in duck, but is not necessarily associated with high lensexpression, as in chicken. These comparative stability studies are being extended to r-crystallinla-enolase and &crystallin/argininosuccinate lyase.
s.151
X ICER Abstracts 4
509
RECRUITMENT OF DETOXIFICATION ENZYMES AS LENS CRYSTALLINS CEPHALOPODS Tomarev. S.. Zfnovieva. R.. Piatmskv. J, National Eye Institute. IHDB. Bethesda, MD. USA
IN
The lenses of cephalopods and vertebrates are a classical example of convergent evolution. In contrast to vertebrates, the major crysrallins (S-crystallins) of the squid and octopus are a family of glutathione S-transferase (GST)-like proteins which are lensspecific and do not appear to possess enzymatic activity, The active GST was purified from the squid digestive gland and isolation of the corresponding gene is now in progress. In octopus there is another lens-specific crystallin (a-crystallin) which is related to aldehyde dehydrogenase (ALDH).n-crystallin is much less abundant in squid. Characterization ofa-crystallin cDNA clones of octopus and squid lens has shown that cephalopod&crystallins are more similar to cytoplasmic and mitochondrial ALDH than to the tumor-inducible and microsonal ALDH of vertebrates. Octopus and squida-crystallins were found to be more similar to each other than to the vertebrate Al.DHs or than the vertebrate ALMS are to each other. cDNA cloning and Northern blotting also provided information about cephalopod cytoskeletal proteins. A relatively abundant intermediate filament-like protein and less abundant Btubulin were found to be lens-specific in the octopus; by contrast, octopus a-tubulin was not lens-specific. Finally, structural and functional studies on 3 squid S-crystallin genes suggested that an overlapping AP-l/anti-oxidative responsive element n~ay be critical for expression of these genes and may have contributed to their recruitment as crystallins during evolution.
5
COMPARATIVE STAJRLITY . STUDIES . . . nstma Voorter. Department of Biochemistry, University Netherlands.
510 ON RNZYMJUCRYSTALLINS . Wrlfned de Jo ” g. of Nijmegen, Nijmegen, The
Lens proteins have, due to their longevity and environmental conditions, extraordinary requirements for structural stability. The finding that several house-keeping enzymes are recruited as eye lens proteins makes it possible to compare stability parameters from these enzym/crystallins in different tissues between species with abundant amounts of this enzyme in their lenses and those without it. We have compared the thermo- and urea-stability of LDH-B4, which is identical with t-crystallin, and abundantly present in lenses of several birds and reptiles. Measuring the thermostability of LDH-Et4 from different sources, the T, values (temperature at which 50% of the enzyme activity remains after a 20’ period) for LDH-B4 from duck heart, duck lens, chicken heart were found to be all around 76 “C, whereas pig heart LDH-B4 was less thermostable, having a T% value of 62 “C. A similar tendency was found with urea inactivation studies. Plotting the first order rate constants obtained from inactivation kinetic plots against the urea concentration it was clear that LDHB4 from pig heart was less stable in urea than the homologous enzymes from duck heart, chicken heart and duck lens. Therefore it is concluded that the avian heart LDH-B is apparently more stable than the homologous enzyme in mammals. This greater stability might make it suitable to function as “crystallin”, as in duck, but is not necessarily associated with high lensexpression, as in chicken. These comparative stability studies are being extended to r-crystallinla-enolase and &crystallin/argininosuccinate lyase.
s.151