title: Adjustments of serine proteases of Daphnia pulex in response to temperature changes.
abstract: Elevated temperatures considerably challenge aquatic invertebrates, and enhanced energy metabolism and protein turnover require adjustments of digestion. In Daphnia, the serine proteases chymotrypsin and trypsin represent the major proteolytic enzymes. Daphnia pulex acclimated to different temperature conditions or subjected to acute heat stress showed increased expression level of serine proteases with rising temperatures. Transcripts of trypsin isoforms were always present in higher amounts than observed for chymotrypsin. Additionally, trypsin isoform transcripts were induced by elevated temperatures to a larger extent. Correspondingly, trypsin activity dominated in cold-acclimated animals. However, the enzymatic activity of chymotrypsin increased at elevated temperatures, whereas trypsin activity slightly decreased, resulting in a shift to dominating chymotrypsin activity in warm-acclimated animals. Zymograms revealed eight bands with proteolytic activity in the range of 20 to 86 kDa. The single bands were assigned to trypsin or chymotrypsin activity applying specific inhibitors or from casein cleavage products identified by mass spectrometric analysis. The total amount of proteolytic activity was elevated with acclimation temperature increase and showed a transient decrease under acute heat stress. The contribution of the different isoforms to protein digestion indicated induction of chymotrypsin with increasing acclimation temperature. For trypsin, the share of one isoform decreased with elevated temperature, while another isoform was enhanced. Thus differential expression of serine proteases was observed in response to chronic and acute temperature changes. The observed phenotypic plasticity adjusts the set of active proteases to the altered needs of protein metabolism optimizing protein digestion for the temperature conditions experienced in the habitat.
authors.affiliation: Institut für Zoophysiologie, Westfälische Wilhelms-Universität, Schlossplatz 8, 48143 Münster, Germany.
authors.forename: Ramona
authors.initials: R
authors.lastname: Dölling
authors.affiliation: Institut für Zoophysiologie, Westfälische Wilhelms-Universität, Schlossplatz 8, 48143 Münster, Germany. Electronic address: D.Becker@bham.ac.uk.
authors.forename: Dörthe
authors.initials: D
authors.lastname: Becker
authors.affiliation: Institut für Biologie und Biotechnologie der Pflanzen, Westfälische Wilhelms-Universität, Schlossplatz 8, 48143 Münster, Germany. Electronic address: susan.hawat@uni-muenster.de.
authors.forename: Susan
authors.initials: S
authors.lastname: Hawat
authors.affiliation: Institut für Zoophysiologie, Westfälische Wilhelms-Universität, Schlossplatz 8, 48143 Münster, Germany.
authors.forename: Marita
authors.initials: M
authors.lastname: Koch
authors.affiliation: Zoological Institute, Cologne Biocentre, University of Cologne, Zülpicher Str. 47b, 50674 Cologne, Germany. Electronic address: Anke.Schwarzenberger1@uni-koeln.de.
authors.forename: Anke
authors.initials: A
authors.lastname: Schwarzenberger
authors.affiliation: Institut für Zoophysiologie, Westfälische Wilhelms-Universität, Schlossplatz 8, 48143 Münster, Germany. Electronic address: zeis@uni-muenster.de.
authors.forename: Bettina
authors.initials: B
authors.lastname: Zeis
mesh_terms: D000064:Acclimatization; D000818:Animals; D060829:Arthropod Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002918:Chymotrypsin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003621:Daphnia / Q000201:enzymology* / Q000254:growth & development / Q000502:physiology; D004063:Digestion; D004790:Enzyme Induction; D004794:Enzyme Repression; D004795:Enzyme Stability; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D005858:Germany; D006358:Hot Temperature / Q000009:adverse effects; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D060106:Lakes; D008970:Molecular Weight; D059748:Proteolysis; D012333:RNA, Messenger / Q000378:metabolism; D013312:Stress, Physiological; D014357:Trypsin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D060829:Arthropod Proteins; D007527:Isoenzymes; D012333:RNA, Messenger; D002918:Chymotrypsin; D014357:Trypsin
keywords: Chymotrypsin; Differential isoform expression; Digestion; Heat stress; Trypsin