title: An active recombinant cocoonase from the silkworm Bombyx mori: bleaching, degumming and sericin degrading activities.
abstract: BACKGROUND
  Cocoonase is a serine protease produced by silk moths and used for softening the cocoons so that they can escape. Degumming is one of the important steps in silk processing. This research aimed to produce an active recombinant Bombyx mori cocoonase (BmCoc) for the silk degumming process.
  
  
  RESULTS
  A recombinant BmCoc was successfully expressed in a Pichia pastoris system. The purified enzyme showed specific activity of 227 U mg(-1) protein, 2.4-fold purification, 95% yield and a molecular weight of 26 kDa. The enzyme exhibited optimal temperature at 40 °C and optimal pH at 8, and showed thermal stability at 25-45 °C and pH stability at 5-9. The recombinant enzyme exhibited sericin degumming ability and color bleaching characteristics, and did not affect the fibroin fiber. The enzyme also degraded sericin substrate with a product size about 30-70 kDa.
  
  
  CONCLUSIONS
  In this study, we successfully produced the active recombinant BmCoc in P. pastoris with promising functions for the Thai silk degumming process, which includes degumming, sericin degrading and color bleaching activities. Our data clearly indicated that the recombinant enzyme had proteolytic activity on sericin but not on fibroin proteins. The recombinant BmCoc has proven to be suitable for numerous applications in the silk industry.
authors.affiliation: Department of Biochemistry, Faculty of Science, Kasetsart University, Bangkok, Thailand; Interdisciplinary Program in Genetic Engineering, The Graduate School, Kasetsart University, Bangkok, Thailand.
authors.forename: Sasimanas
authors.initials: S
authors.lastname: Unajak
authors.forename: Suradet
authors.initials: S
authors.lastname: Aroonluke
authors.forename: Amornrat
authors.initials: A
authors.lastname: Promboon
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D012831:Bombyx / Q000201:enzymology* / Q000378:metabolism; D003116:Color; D005349:Fibroins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D019476:Insect Proteins / Q000378:metabolism; D008970:Molecular Weight; D010843:Pichia / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D047030:Sericins / Q000378:metabolism*; D057057:Serine Proteases / Q000737:chemistry / Q000378:metabolism*; D047011:Silk / Q000378:metabolism*; D013696:Temperature; D013783:Textile Industry / Q000379:methods*
chemical_list: D019476:Insect Proteins; D011994:Recombinant Proteins; D047030:Sericins; D047011:Silk; D005349:Fibroins; D057057:Serine Proteases
keywords: Bombyx mori; bleaching; cocoonase; degumming; sericin degrading; yeast expression system