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Homologous modeling of the lysosomal protective protein/carboxypeptidase L: Structural and functional implications of mutations identified in galactosialidosis patients
Author(s) -
Elsliger MarcAndré,
Potier Michel
Publication year - 1994
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.340180110
Subject(s) - cathepsin a , carboxypeptidase , homology modeling , biochemistry , active site , missense mutation , catalytic triad , chemistry , mutant , mutation , protein secondary structure , protein structure , biology , stereochemistry , genetics , enzyme , gene , cathepsin b
The deficiency of the lysosomal protective protein/carboxypeptidase L (CARB L) causes the lysosomal storage disorder, galactosialidosis, characterized by neuraminidase and β‐galactosidase deficiencies in patients' cells. The three enzymes form a complex inside the lysosome, and the neuraminidase and β‐galactosidase deficiencies are secondary to CARB L deficiency. Sequence similarity and common enzymological properties suggest that the protomeric tertiary structure of CARB L is conserved within a family of serine carboxypeptidases which includes the yeast carboxypeptidase Y, killer expression I gene product and several plant carboxypeptidases. We used this homology to build a model of the CARB L structure based on the recently published X‐ray atomic coordinates of the wheat carboxypeptidase II (CPDW‐II) which shares 32% primary structure identity with CARB L. Small insertions and deletions were accommodated into the model structure by energy minimization using the DREIDING II force field. The Cα atomic‐coordinates of the final CARB L model have a RMS shift of 1.01 Å compared to the corresponding conserved residues in the CPDW‐II template structure. The correct orientation of the homologous catalytic triad residues Ser150, His429 and Asp392, the potential energy calculations and the distribution of hydrophobic and hydrophillic residues in the structure all support the validity of the CARB L model. Most missense mutations identified in galactosialidosis patients were located in secondary structural elements except for the Tyr211→Asn mutation which is in a loop. The other mutant residues have their side chains deeply buried in the central β‐sheet of the model structure except for the Phe412→Val mutation which is located in the dimer interface. The predicted effects of specific mutations on CARB L structural stability correlates well with recently published transient expression studies of mutant CARB L (Shimmoto, M. et al., J. Clin. Invest., 91:2393–2399, 1993). © 1994 John Wiley & Sons, Inc.