title: Extended bottom-up proteomics with secreted aspartic protease Sap9.
abstract: We investigate the benefits and experimental feasibility of approaches enabling the shift from short (1.7 kDa on average) peptides in bottom-up proteomics to about twice longer (~3.2 kDa on average) peptides in the so-called extended bottom-up proteomics. Candida albicans secreted aspartic protease Sap9 has been selected for evaluation as an extended bottom-up proteomic-grade enzyme due to its suggested dibasic cleavage specificity and ease of production. We report the extensive characterization of Sap9 specificity and selectivity revealing that protein cleavage by Sap9 most often occurs in the vicinity of proximal basic amino acids, and in select cases also at basic and hydrophobic residues. Sap9 is found to cleave a large variety of proteins in a relatively short, ~1 h, period of time and it is efficient in a broad pH range, including slightly acidic, e. g., pH5.5, conditions. Importantly, the resulting peptide mixtures contain representative peptides primarily in the target 3-7 kDa range. The utility and advantages of this enzyme in routine analysis of protein mixtures are demonstrated and the limitations are discussed. Overall, Sap9 has a potential to become an enzyme of choice in an extended bottom-up proteomics, which is technically ready to complement the traditional bottom-up proteomics for improved targeted protein structural analysis and expanded proteome coverage.
  
  
  CONCLUSIONS
  Advances in biological applications of mass spectrometry-based bottom-up proteomics are oftentimes limited by the extreme complexity of biological samples, e.g., proteomes or protein complexes. One of the reasons for it is in the complexity of the mixtures of enzymatically (most often using trypsin) produced short (<3 kDa) peptides, which may exceed the analytical capabilities of liquid chromatography and mass spectrometry. Information on localization of protein modifications may also be affected by the small size of typically produced peptides. On the other hand, advances in high-resolution mass spectrometry and liquid chromatography have created an intriguing opportunity of improving proteome analysis by gradually increasing the size of enzymatically-derived peptides in MS-based bottom-up proteomics. Bioinformatics has already confirmed the envisioned advantages of such approach. The remaining bottle-neck is an enzyme that could produce longer peptides. Here, we report on the characterization of a possible candidate enzyme, Sap9, which may be considered for producing longer, e.g., 3-7 kDa, peptides and lead to a development of extended bottom-up proteomics.
authors.affiliation: Biomolecular Mass Spectrometry Laboratory, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors.forename: Ünige A
authors.initials: ÜA
authors.lastname: Laskay
authors.affiliation: Biomolecular Mass Spectrometry Laboratory, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
authors.forename: Kristina
authors.initials: K
authors.lastname: Srzentić
authors.affiliation: Department of Dermatology, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland.
authors.forename: Michel
authors.initials: M
authors.lastname: Monod
authors.affiliation: Biomolecular Mass Spectrometry Laboratory, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland. Electronic address: yury.tsybin@epfl.ch.
authors.forename: Yury O
authors.initials: YO
authors.lastname: Tsybin
mesh_terms: D000595:Amino Acid Sequence; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry*; D001665:Binding Sites; D004789:Enzyme Activation; D004795:Enzyme Stability; D005656:Fungal Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D010449:Peptide Mapping / Q000379:methods*; D011485:Protein Binding; D020539:Sequence Analysis, Protein / Q000379:methods*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D005656:Fungal Proteins; D016282:Aspartic Acid Endopeptidases; C116371:Sap9 protein, Candida albicans
keywords: Bottom-up proteomics; Enzymatic digestion; Extended bottom-up proteomics; High-resolution mass spectrometry; Middle-down proteomics