Blog
Tabulate expression data from multiple analyses with Mascot Daemon
Studies that use mass spectrometry-based quantitation often contain large numbers of individual analyses: samples from different sources or treatments or time points, possibly fractionated, with replicates and so forth. Using statistical methods to combine the analyses, extract meaningful information, and report it as charts and tables is a complex task that usually requires custom scripting in a language such as [...]
Human Proteome Project data interpretation guidelines
The Human Proteome Project (HPP) data interpretation guidelines were recently updated. Many of the guidelines are good practice and common sense in any proteomics study where reliable protein identification is critical, not just when studying the human proteome. The guidelines are easy to meet using Mascot Server 2.7. Core guidelines The full list consists of 9 guidelines. The first one [...]
How to set up remote working
There are times when you unexpectedly find yourself having to work from home. Fear not: data analysis doesn’t need to stop when you’re away from the lab. Mascot Server has a client-server architecture, and the client PC can be located anywhere. Distiller and Daemon can also be used remotely, or they can be run on a remote client PC and [...]
Disulfide bond characterisation
Support for matching crosslinked peptides is a new feature in Mascot Server 2.7. The following linkage types can be detected: intralinks – the linked peptides are from the same protein interlinks – the linked peptides are from two different proteins looplinks – connecting two amino acids within a single peptide monolinks – a linker with one end attached and the [...]
The Third Column: MS/MS fragment ion decharging in Mascot Server 2.7
In the Mascot Generic (mgf) peak list format, MS/MS fragment ions are typically defined as pairs of values. The first value is the m/z of the fragment ion peak and the second the intensity of the peak. However, a third value can also be supplied – the charge state of the fragment ion. In Mascot 2.6 or earlier, the fragment [...]
Protein FDR in Mascot Server 2.7
One of the new features in Mascot Server 2.7, now running on this web site, is an estimate of protein FDR. This is displayed in the Protein Family Summary for Fasta searches whenever automatic decoy is selected. The basis is the number of proteins inferred in the target database compared with the number in the decoy database. Conceptually, this is [...]
Disaster recovery
There are a number of potential issues that can cause your Mascot Server or other computer infrastructure to stop working. In the worst case, you may need to do a full recovery from backups. This can be an involved procedure, but it is straightforward as long as you have backed up key configuration and data files. For disk or storage [...]
Is your database search reproducible?
A lot has been written about the reproducibility of shotgun proteomics workflows, as well as controlling measurement variability between instruments and laboratories. An equally important factor is data analysis transparency and reproducibility, which is gaining increasing visibility. This boils down to two essentials: recording all software parameters used, and ensuring the software produces the same output given the same input [...]
Common myths about protein scores
Mascot Server is used in many different application areas by both mass spectrometry experts and non-experts. Over the years, we’ve spotted a few recurring misconceptions about how protein scores are interpreted and used. All the examples come from recent peer-reviewed papers. Protein scores in PMF searches The very first thing to check is, what type of experiment is being reported. [...]
The three Ds: Diethylation, Dimethylation and the Deuterium effect
Dimethylation Mascot Server and Mascot Distiller support a number of precursor intensity based quantitation techniques using a number of different techniques and chemistries. The software also allows you to flexibly define your own methods, allowing you to implement quantitation protocols which we have not supplied ‘out of the box’. One isotope labelling method which Distiller supports ‘out of the box’ [...]
Identify proteins by more than ‘gut’ feeling
Last month, we discussed benchmarking protein inference and the role of shared peptide matches. Excluding shared matches may be beneficial to protein identification accuracy if the sequence database contains perfect representations of all proteins in the sample. Many real-life data sets don’t meet this condition. Metaproteomics and environmental samples, such as the various human body sites, peat bog and ocean [...]
What are you inferring?
Benchmarking protein inference is notoriously difficult. Artificial samples of known content tend to be too simple while real samples lack ground truth. An interesting approach was adopted for the ABRF iPRG 2016 study, and has been the subject of a publication from The et al. A collection of human Protein Epitope Signature Tags (PrESTs) were expressed in E. coli and [...]
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