X-ray crystallography and structural stability of digestive  lysozyme from cow stomach.
In ruminants, some leaf-eating animals, and some insects, defensive lysozymes have been adapted to become digestive enzymes, in order to digest bacteria in the stomach. Digestive lysozyme has been reported to be resistant to protease and to have optimal activity at acidic pH. The structural basis of the adaptation providing persistence of lytic activity under severe gastric conditions remains unclear. In this investigation, we obtained the crystallographic structure of recombinant bovine stomach lysozyme 2 (BSL2). Our denaturant and thermal unfolding experiments revealed that BSL2 has high conformational stability at acidic pH. The high stability in acidic solution could be related to pepsin resistance, which has been previously reported for BSL2. The crystal structure of BSL2 suggested that negatively charged surfaces, a shortened loop and salt bridges could provide structural stability, and thus resistance to pepsin. It is likely that BSL2 loses lytic activity at neutral pH because of adaptations to resist pepsin.
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido, Japan.
Yasuhiro
Y
Nonaka
Daisuke
D
Akieda
Tomoyasu
T
Aizawa
Nobuhisa
N
Watanabe
Masakatsu
M
Kamiya
Yasuhiro
Y
Kumaki
Mineyuki
M
Mizuguchi
Takashi
T
Kikukawa
Makoto
M
Demura
Keiichi
K
Kawano
D000818:Animals; D002417:Cattle; D018360:Crystallography, X-Ray; D019791:Guanidine / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013270:Stomach / Q000201:enzymology*
D011994:Recombinant Proteins; D009113:Muramidase; D019791:Guanidine