Discussion

Leishmania species parasite infections, termed the leishmaniases, cause significant global infectious disease burden. The lifecycle of the parasite embodies three main stages that require precise coordination of gene regulation to survive drastic environmental shifts transitioning from sandfly to mammalian hosts. Constitutive transcription in these kinetoplastid parasites is overwhelmingly reliant on post-transcriptional mechanisms, yet strikingly few Leishmania trans-regulator proteins are known. Utilizing optimised crosslinking and in-depth, quantified mass spectrometry, we present a comprehensive analysis of over 1,400 mRNA binding proteins (mRBPs) and over 2,400 whole cell proteins from the three main lifecycle stages. Supporting the validity of this RBPome, Gene Ontology (GO) analysis reveals significant enrichment of RNA binding and gene regulation terms and endogenously-tagged candidate mRBPs exhibit stage-specific expression and associate with mRNA. Important findings from this work include a low correlation between protein and transcript expression, stage-specific variation in protein expression versus mRNA binding potential, and a modulation of mRNA binding protein enrichment during the Leishmania parasite lifecycle. Our results indicate that in L.mexicana parasites, RNA levels are not a strong predictor of whole cell expression or RNA binding potential of proteins. Our study is the first at its depth in kinetoplastid parasites and provides novel, quantified insight into trans-regulatory mRNA:Protein (mRNP) complexes that drive Leishmania lifecycle progression to human infectious stages.