title: Structure-function analysis of grass clip serine protease involved in Drosophila Toll pathway activation.
abstract: Grass is a clip domain serine protease (SP) involved in a proteolytic cascade triggering the Toll pathway activation of Drosophila during an immune response. Epistasic studies position it downstream of the apical protease ModSP and upstream of the terminal protease Spaetzle-processing enzyme. Here, we report the crystal structure of Grass zymogen. We found that Grass displays a rather deep active site cleft comparable with that of proteases of coagulation and complement cascades. A key distinctive feature is the presence of an additional loop (75-loop) in the proximity of the activation site localized on a protruding loop. All biochemical attempts to hydrolyze the activation site of Grass failed, strongly suggesting restricted access to this region. The 75-loop is thus proposed to constitute an original mechanism to prevent spontaneous activation. A comparison of Grass with clip serine proteases of known function involved in analogous proteolytic cascades allowed us to define two groups, according to the presence of the 75-loop and the conformation of the clip domain. One group (devoid of the 75-loop) contains penultimate proteases whereas the other contains terminal proteases. Using this classification, Grass appears to be a terminal protease. This result is evaluated according to the genetic data documenting Grass function.
authors.affiliation: Architecture et Fonction des Macromolécules Biologiques UMR6098, Parc Scientifique et Technologique de Luminy, 13288 Marseille Cedex 09, France. Christine.Kellenberger@afmb.univ-mrs.fr
authors.forename: Christine
authors.initials: C
authors.lastname: Kellenberger
authors.forename: Philippe
authors.initials: P
authors.lastname: Leone
authors.forename: Laurent
authors.initials: L
authors.lastname: Coquet
authors.forename: Thierry
authors.initials: T
authors.lastname: Jouenne
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Reichhart
authors.forename: Alain
authors.initials: A
authors.lastname: Roussel
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D002460:Cell Line; D004330:Drosophila; D029721:Drosophila Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D057057:Serine Proteases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013329:Structure-Activity Relationship; D051193:Toll-Like Receptors / Q000235:genetics / Q000378:metabolism*
chemical_list: D029721:Drosophila Proteins; D051193:Toll-Like Receptors; D057057:Serine Proteases