iota-Carrageenases constitute a novel family of glycoside hydrolases, unrelated to that of kappa-carrageenases.
iota-Carrageenases are polysaccharide hydrolases that cleave the beta-1,4 linkages between the d-galactose-4-sulfate and 3, 6-anhydro-d-galactose-2-sulfate residues in the red algal galactans known as iota-carrageenans. We report here on the purification of iota-carrageenase activity from the marine bacterium Zobellia galactanovorans and on the characterization of iota-carrageenase structural genes. Genomic libraries from this latter bacterium as well as from Alteromonas fortis were functionally screened for the presence of iota-carrageenase(+) clones. The Z. galactanovorans and A. fortis iota-carrageenase genes encode homologous proteins of 53.4 and 54.8 kDa, respectively. Based on hydrophobic cluster analysis and on the (1)H NMR monitoring of the products of the overexpressed A. fortis iota-carrageenase, these enzymes appear to form a new family of glycoside hydrolases, unrelated to that of kappa-carrageenases and with an inverting mechanism of hydrolysis. They both feature a 45-amino acid-long N-terminal segment with sequence similarity to the N-terminal region of several other polysaccharidases. In those for which a three-dimensional structure is available, this conspicuous segment, also deemed "glycanase motif" (Chua, J. E. H., Manning, P. A., and Morona, R. (1999) Microbiology (Reading) 145, 1649-1659), corresponds to a strand-helix-strand "cap" that covers the N-terminal end of a common, right-handed beta-helical fold.
Barbeyron
T
T
Station Biologique de Roscoff, UMR 1931 (CNRS and Laboratoires Goëmar), Place Georges Teissier, 29680 Roscoff, Bretagne, France.
Michel
G
G
Potin
P
P
Henrissat
B
B
Kloareg
B
B
D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D001665:Binding Sites; D002474:Cell-Free System; D003001:Cloning, Molecular; D016000:Cluster Analysis; D004591:Electrophoresis, Polyacrylamide Gel; D015723:Gene Library; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000145:classification / Q000302:isolation & purification; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D000461:Rhodophyta / Q000201:enzymology*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
D001426:Bacterial Proteins; D011994:Recombinant Proteins; D006026:Glycoside Hydrolases; C019846:kappa-carrageenase protein, Alteromonadaceae