title: Crystal structure of a fungal protease inhibitor from Antheraea mylitta.
abstract: Indian tasar silk is produced by a wild insect called Antheraea mylitta. Insects do not have any antigen-antibody mediated immune system like vertebrates but they produce a wide variety of effector proteins and peptides possessing potent antifungal and antibacterial activity to combat microbial attack. Antheraea mylitta expresses a fungal protease inhibitor AmFPI-1, in the hemolymph that inhibits alkaline protease of Aspergillus oryzae for protection against fungal infection. AmFPI-1 is purified from the hemolymph, crystallized and the structure is solved using the single isomorphous replacement with anomalous scattering (SIRAS) method to a resolution of 2.1 A. AmFPI-1 is a single domain protein possessing a unique fold that consists of three helices and five beta strands stabilized by a network of six disulfide bonds. The reactive site of AmFPI-1 is located in the loop formed by residues 46-66, wherein Lys54 is the P(1) residue. Superimposition of the loop with reactive sites of other canonical protease inhibitors shows that reactive site conformation of AmFPI-1 is similar to them. The structure of AmFPI-1 provides a framework for the docking of a 1:1 complex between AmFPI-1 and alkaline protease. This study addresses the structural basis of AmFPI-1's specificity towards a fungal serine protease but not to mammalian trypsin and may help in designing specific inhibitors against fungal proteases.
authors.affiliation: Department of Biotechnology, Indian Institute of Technology, Kharagpur 721302, India.
authors.forename: Sobhan
authors.initials: S
authors.lastname: Roy
authors.forename: Penmatsa
authors.initials: P
authors.lastname: Aravind
authors.forename: Chaithanya
authors.initials: C
authors.lastname: Madhurantakam
authors.forename: Ananta Kumar
authors.initials: AK
authors.lastname: Ghosh
authors.forename: Rajan
authors.initials: R
authors.lastname: Sankaranarayanan
authors.forename: Amit Kumar
authors.initials: AK
authors.lastname: Das
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000935:Antifungal Agents / Q000737:chemistry* / Q000302:isolation & purification; D001236:Aspergillus oryzae / Q000201:enzymology; D001665:Binding Sites; D002712:Chlorides / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D005658:Fungi / Q000201:enzymology; D006458:Hemolymph / Q000737:chemistry; D006860:Hydrogen Bonding; D019476:Insect Proteins / Q000737:chemistry* / Q000302:isolation & purification; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009036:Moths / Q000737:chemistry*; D017671:Platinum Compounds / Q000737:chemistry; D011480:Protease Inhibitors / Q000737:chemistry* / Q000302:isolation & purification; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000737:chemistry; D013381:Subtilisins / Q000037:antagonists & inhibitors / Q000737:chemistry; D014357:Trypsin / Q000737:chemistry
chemical_list: D000935:Antifungal Agents; D002712:Chlorides; C541006:FPI-1 protease inhibitor, Antheraea mylitta; D019476:Insect Proteins; D017671:Platinum Compounds; D011480:Protease Inhibitors; C036919:tetrachloroplatinate; D012697:Serine Endopeptidases; D013381:Subtilisins; D014357:Trypsin; C026109:oryzin