| 1. |
- Rosengren, Anna, et al.
(författare)
-
The role of subsite +2 of the Trichoderma reesei beta-mannanase TrMan5A in hydrolysis and transglycosylation
- 2012
-
Ingår i: Biocatalysis and Biotransformation. - : Informa UK Limited. - 1024-2422 .- 1029-2446. ; 30:3, s. 338-352
-
Tidskriftsartikel (refereegranskat)abstract
- The N-terminal catalytic module of beta-mannanase TrMan5A from the filamentous fungus Trichoderma reesei is classified into family 5 of glycoside hydrolases. It is further classified in clan A with a (beta/alpha)(8) barrel configuration and has two catalytic glutamates (E169 and E276). It has at least five other residues conserved in family 5. Sequence alignment revealed that an arginine (R171 in TrMan5A) is semi-conserved among beta-mannanases in family 5. In a previously published mannobiose complex structure, this residue is positioned in hydrogen bonding distance from the C2 hydroxyl group of the mannose residue bound at the +2 subsite. To study the function of R171, mutants of this residue were constructed. The results show that arginine 171 is important for substrate binding and transglycosylation. A mutant of TrMan5A with the substitution R171K displayed retained activity on polymeric galactomannan but reduced activity on oligosaccharides due to an increase of K-m. While the wild-type enzyme produces mannobiose as dominant product from mannotetraose the R171K mutant shows an altered product profile, producing mannotriose and mannose. The cleavage pattern of mannotetraose was analysed with a method using isotope labelled water ((H2O)-O-18) and mass spectrometry which showed that the preferred productive binding mode of mannotetraose was shifted from subsite -2 to +2 in the wild-type to subsite -3 to +1 in the R171K mutant. Significant differences in product formation after manno-oligosaccharide incubation showed that the wild-type enzyme can perform transglycosylation on to saccharide acceptors while the R171K mutant cannot, likely due to loss of acceptor affinity. Interestingly, both enzymes show the ability to perform alcoholysis reactions with methanol and butanol, forming new beta-linked glyco-conjugates. Furthermore, it appears that the wild-type enzyme produces mainly mannobiose conjugates using M-4 as substrate, while in contrast the R171K mutant produces mainly mannotriose conjugates, due to the altered subsite binding.
|
|
| 2. |
- Söderberg, Christopher, et al.
(författare)
-
Detection of Crosslinks within and between Proteins by LC-MALDI-TOFTOF and the Software FINDX to Reduce the MSMS-Data to Acquire for Validation.
- 2012
-
Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:6
-
Tidskriftsartikel (refereegranskat)abstract
- Lysine-specific chemical crosslinking in combination with mass spectrometry is emerging as a tool for the structural characterization of protein complexes and protein-protein interactions. After tryptic digestion of crosslinked proteins there are thousands of peptides amenable to MSMS, of which only very few are crosslinked peptides of interest. Here we describe how the advantage offered by off-line LC-MALDI-TOF/TOF mass spectrometry is exploited in a two-step workflow to focus the MSMS-acquisition on crosslinks mainly. In a first step, MS-data are acquired and all the peak list files from the LC-separated fractions are merged by the FINDX software and screened for presence of crosslinks which are recognized as isotope-labeled doublet peaks. Information on the isotope doublet peak mass and intensity can be used as search constraints to reduce the number of false positives that match randomly to the observed peak masses. Based on the MS-data a precursor ion inclusion list is generated and used in a second step, where a restricted number of MSMS-spectra are acquired for crosslink validation. The decoupling of MS and MSMS and the peptide sorting with FINDX based on MS-data has the advantage that MSMS can be restricted to and focused on crosslinks of Type 2, which are of highest biological interest but often lowest in abundance. The LC-MALDI TOF/TOF workflow here described is applicable to protein multisubunit complexes and using (14)N/(15)N mixed isotope strategy for the detection of inter-protein crosslinks within protein oligomers.
|
|
