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Posted by John Cottrell (April 17, 2017)

Mascot Security: priority settings

An earlier article looked at privacy settings in Mascot security. This article looks at priority settings; the settings that allow one user group to run bigger or longer or more complex searches than another. Many aspects of searches can be limited by user group. The important ones are: SEARCH: Allow msms no enzyme searches SEARCH: Maximum number of concurrent searches [...]

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Posted by John Cottrell (March 15, 2017)

Mascot Security: privacy settings

It is perfectly possible to share a single Mascot Server between individuals or groups who require privacy for their searches. Mascot Security provides the mechanism to limit access to result reports, databases, and even custom modifications. Mascot security is not designed to be highly secure – a determined hacker could probably find ways around it without too much difficulty – [...]

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Posted by John Cottrell (February 15, 2017)

Exporting search results: tips and tricks

The Mascot Server export utility allows search results to be exported in a wide range of formats, together with the native result file and the MGF peak list. Exporting the result file can be useful if you need it for a third party application and don’t have file share access to the Mascot Server. Exporting the MGF might be useful [...]

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Posted by Patrick Emery (January 16, 2017)

How many of you are there in there? Processing and searching chimeric MS/MS spectra with Mascot Distiller and Mascot Server

In the typical shotgun proteomics experiment, the assumption is that each MS/MS spectrum is derived from a single precursor selected by the Mass Spectrometer for fragmentation. However, in practice, near isobaric precursors can co-elute and undergo co-fragmentation resulting in chimeric MS/MS spectra containing fragments from multiple different precursor peptides. With high resolution data, it is possible for these overlapping isotope [...]

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Posted by John Cottrell (December 13, 2016)

Protein inference for spectral library searches

The major new feature of Mascot Server 2.6, now running on this web site, is that searches of spectral libraries have been fully integrated with ‘conventional’ Mascot searches of Fasta files. The search engine for spectral library searches is MSPepSearch from Steve Stein and colleagues at NIST. We didn’t have any revolutionary ideas for improving spectral library scoring so, rather [...]

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Posted by Richard Jacob (November 14, 2016)

Benchmarking your Mascot Server

In an earlier blog post we talked about choosing the right hardware for a Mascot Server and mentioned that the major performance bottle neck is the CPU performance. We also looked at the PassMark PerformanceTest CPUBenchmark as a way of predicting the performance of a Mascot Server. In this article we will look at how to measure Mascot Server performance [...]

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Posted by John Cottrell (October 19, 2016)

Retention time

Although retention time is not part of the Mascot scoring algorithm, it can be used by Percolator to improve the re-scoring of search results and it is important or essential information for many types of quantitation. This article examines how retention time is represented in the peak list, the search results, and various export formats. Mascot Server works off a [...]

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Posted by Richard Jacob (September 14, 2016)

Getting the most out of your Mascot Server hardware

A Mascot Server search consists of a number of separate stages. Once the input file has been uploaded to the server, Mascot starts by sorting the peak list by peptide molecular mass. Unless the peak list is very small, it also divides the peak list into chunks limited in size by either the number of bytes or the number of [...]

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Posted by Patrick Emery (August 18, 2016)

Not Better Together: Processing and searching combined CID+ETD datasets with Mascot Distiller 2.6

Many modern mass spectrometers will produce raw datasets containing more than one type of scan data. For example, a common experiment using a Thermo Orbitrap instrument is to select the most abundant precursor ions and either independently fragment them using both ETD and CID fragmentation, or use a decision tree to select different fragmentation methods depending on, for example, the [...]

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Posted by David Creasy (July 18, 2016)

Improved security for Mascot Installations under Linux

In the manual, we recommend (because it is easiest) that ms-monitor.exe is run as root. However, a more secure arrangement is to run ms-monitor.exe as a less privileged user. By default, Apache cgi processes run as www-data:www-data, and for most distros, this is set in the envvars file: export APACHE_RUN_USER=www-data export APACHE_RUN_GROUP=www-data This can however, be overriden in the /etc/apache2/apache2.conf [...]

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Posted by John Cottrell (June 18, 2016)

High FDRs for methylated peptides III

The MCP paper "Large Scale Mass Spectrometry-based Identifications of Enzyme-mediated Protein Methylation Are Subject to High False Discovery Rates" raises some important questions concerning the accuracy and interpretation of database search results. In this third article, we look at the difference between using counts of matches (PSMs) and counts of distinct sequences to calculate the false discovery rate (FDR). filestarget [...]

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Posted by John Cottrell (May 18, 2016)

High FDRs for methylated peptides II

In a previous article, we discussed how the false discovery rate (FDR) for modified peptides would be higher than the global FDR for all PSMs if the proportion of modified peptides in the search space for false matches was higher than for true matches. This is only one factor in the very high FDRs for methylated peptides reported in the [...]

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