Encompassing new use cases - level 3.0 of the HUPO-PSI format for molecular interactions

BACKGROUND

Systems biologists study interaction data to understand the behaviour of whole cell systems, and their environment, at a molecular level. In order to effectively achieve this goal, it is critical that researchers have high quality interaction datasets available to them, in a standard data format, and also a suite of tools with which to analyse such data and form experimentally testable hypotheses from them. The PSI-MI XML standard interchange format was initially published in 2004, and expanded in 2007 to enable the download and interchange of molecular interaction data. PSI-XML2.5 was designed to describe experimental data and to date has fulfilled this basic requirement. However, new use cases have arisen that the format cannot properly accommodate. These include data abstracted from more than one publication such as allosteric/cooperative interactions and protein complexes, dynamic interactions and the need to link kinetic and affinity data to specific mutational changes.

RESULTS

The Molecular Interaction workgroup of the HUPO-PSI has extended the existing, well-used XML interchange format for molecular interaction data to meet new use cases and enable the capture of new data types, following extensive community consultation. PSI-MI XML3.0 expands the capabilities of the format beyond simple experimental data, with a concomitant update of the tool suite which serves this format. The format has been implemented by key data producers such as the International Molecular Exchange (IMEx) Consortium of protein interaction databases and the Complex Portal.

CONCLUSIONS

PSI-MI XML3.0 has been developed by the data producers, data users, tool developers and database providers who constitute the PSI-MI workgroup. This group now actively supports PSI-MI XML2.5 as the main interchange format for experimental data, PSI-MI XML3.0 which additionally handles more complex data types, and the simpler, tab-delimited MITAB2.5, 2.6 and 2.7 for rapid parsing and download.

Nutrient sensing systems for rapid activation of the protein kinase A pathway in yeast

The cAMP-protein kinase A (PKA) pathway in the yeast Saccharomyces cerevisiae controls a variety of properties that depend on the nutrient composition of the medium. High activity of the pathway occurs in the presence of rapidly fermented sugars like glucose or sucrose, but only as long as growth is maintained. Growth arrest of fermenting cells or growth on a respiratory carbon source, like glycerol or ethanol, is associated with low activity of the PKA pathway. We have studied how different nutrients trigger rapid activation of the pathway. Glucose and sucrose activate cAMP synthesis through a G-protein-coupled receptor system, consisting of the GPCR Gpr1, the Galpha protein Gpa2 and its RGS protein Rgs2. Glucose is also sensed intracellularly through its phosphorylation. Specific mutations in Gpr1 abolish glucose but not sucrose signalling. Activation of the PKA pathway by addition of a nitrogen source or phosphate to nitrogen- or phosphate-starved cells, respectively, is not mediated by an increase in cAMP. Activation by amino acids is triggered by the general amino acid permease Gap1, which functions as a transporter/receptor. Short truncation of the C-terminus results in constitutively activating alleles. Activation by ammonium uses the ammonium permeases Mep1 and Mep2 as receptor. Specific point mutations in Mep2 uncouple signalling from transport. Activation by phosphate is triggered a.o. by the Pho84 phosphate permease. Several mutations in Pho84 separating transport and signalling or triggering constitutive activation have been obtained.