MeSH Headings for GPCRs Untangled for Effective PubMed Searches

What is MeSH?

The Medical Subject Headings (MeSH) thesaurus produced by the National Library of Medicine is a hierarchically organized vocabulary used to index, catalog, and search biomedical and health-related information in MEDLINE/PubMed. MeSH headings form a tree structure with many branches, and each branch has many levels of sub-branches. One can search PubMed efficiently by using appropriate MeSH terms instead of randomly trying one set of keywords after another or desperately peppering search terms with wildcards. Excellent tutorials are found here.

Pitfalls

Some MeSH terms appear in multiple branches for good reasons. For instance, a heading Receptors, neuropeptide is mapped under Receptors, neurotransmitter and Receptors, peptide at the same time since both are reasonable generalizations of its characteristics. However, that classification strategy sometimes creates a mess and trap PubMed users. To give an example, let's look at purinergic receptors. Purinergic P2Y receptors are a subgroup of G protein-coupled receptors (GPCRs). There are also purinergic ion channels called P2X receptors. Understandably, these structurally unlike but functionally close groups of proteins are aggregated into Receptors, purinergic, but who can imagine that that Receptors, purinergic occupies a position in the Receptors, G-Protein-Coupled domain and contaminates it with ion channels! It is like classifying dolphins into fish because fish are finned creatures and dolphins have fins, too.

Another source of confusion is that the MeSH tree for GPCRs is somewhat busy, with a maximum of five branches from the GPCR kingdom at the top to the narrowest concept. Moreover, the ranks of MeSH headings are arbitrary and do not necessarily indicate their granularity; for instance, while PAR-2 receptor and β1-adrenoceptor are individual proteins, the former is in the second rank, and the latter in the fifth. Similarly, the tip of a branch can be a group, a subgroup, a protein, or something in between. This complexity contrasts with the simple taxonomy developed by Guide to Pharmacology (G2P), which consists of only three layers, the GPCR kingdom—receptor families—individual receptors, and looks more familiar to biologists.

Solution

To help search PubMed effectively, We have aligned the MeSH thesaurus for GPCRs with G2P's taxonomy (Table below). Indention indicates branching from higher-order headings. The terms in same row are meant to be the closest concepts, if not identical, from MeSH and G2P. Interestingly, Proto-Oncogene Mas, or MAS1, belongs to different groups, i.e., angiotensin receptors and class A orphans. That may serve as another pitfall if one takes either classification for granted while unaware of the other.

Table. GPCR MeSH headings aligned with G2P taxonomy

MeSH headings and Guide to Pharmacology taxonomy were retrieved on December 2, 2021, and November 21, 2021, respectively.

NB the table may not be displayed correctly on a tablet or a smartphone.