Susceptibility of mammalian deoxyribonucleases I (DNases I) to proteolysis by proteases and its relationships to tissue distribution: biochemical and molecular analysis of equine DNase I.
Equine (Equus caballus) deoxyribonuclease I (DNase I) was purified from the parotid gland, and its 1295-bp cDNA was cloned. The mature equine DNase I protein consisted of 260 amino acid residues. The enzymatic properties and structural aspects of the equine enzyme were closely similar to those of other mammalian DNases I. Mammalian DNases I are classified into three types--pancreatic, parotid and pancreatic-parotid-based on their tissue distribution; as equine DNase I showed the highest activity in the parotid gland, it was confirmed to be of the parotid-type. Comparison of the susceptibility of mammalian DNases I to proteolysis by proteases demonstrated a marked correlation between tissue distribution and sensitivity/resistance to proteolysis; pancreatic-type DNase I shared properties of resistance to proteolysis by trypsin and chymotrypsin, whereas parotid-type DNase I did not. In contrast, pancreatic-parotid-type DNase I exhibited resistance to proteolysis by pepsin, whereas the other enzyme types did not. However, site-directed mutagenesis analysis revealed that only a single amino acid substitution could not account for acquisition of proteolysis resistance in the mammalian DNase I family during the course of molecular evolution. These properties are compatible with adaptation of mammalian DNases I for maintaining their activity in vivo.
Ueki
Misuzu
M
Division of Medical Genetics and Biochemistry, Faculty of Medical Sciences, University of Fukui, Eiheiji, Fukui 910-1193, Japan.
Takeshita
Haruo
H
Fujihara
Junko
J
Ueta
Gen
G
Nakajima
Tamiko
T
Kominato
Yoshihiko
Y
Kishi
Koichiro
K
Iida
Reiko
R
Yasuda
Toshihiro
T
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002918:Chymotrypsin / Q000737:chemistry*; D003850:Deoxyribonuclease I / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D006736:Horses; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009928:Organ Specificity; D010179:Pancreas / Q000737:chemistry* / Q000201:enzymology; D010306:Parotid Gland / Q000737:chemistry* / Q000201:enzymology; D010802:Phylogeny; D016415:Sequence Alignment; D013045:Species Specificity; D013379:Substrate Specificity; D014357:Trypsin / Q000737:chemistry*
D003850:Deoxyribonuclease I; D002918:Chymotrypsin; D014357:Trypsin