In order to obtain orthologs for human genes, I am working with InParanoid version 7.0. This version of the database uses Ensembl Protein Identifiers (ENSP) from ENSEMBL version v54, which is based on NCBI 36 assembly of the human genome.
For my project, I need to have the Ensembl Gene Identifiers (ENSG) of these proteins, but in the last version of ENSEMBL, which is based on GRCh38 assembly. I need to use this version of InParanoid for consistency with previous analyzes.
Thus, my question is, could I just use biomaRt to map ENSP (from NCBI36) to ENSG (actual version) or this approach is inherently wrong?
Is it possible to "convert" ENSP identifiers from NCBI36 to GRCh38 and then do the map to ENSG?. I am aware of liftOver but I am not sure it would work here.