Extracellular release of two peptidases dominates generation of the trypanosome quorum-sensing signal

Abstract

Trypanosomes causing African sleeping sickness use quorum-sensing (QS) to generate transmission-competent stumpy forms in their mammalian hosts. This density-dependent process is signalled by oligopeptides that stimulate the signal transduction pathway leading to stumpy formation. Using mass spectrometry analysis, peptidases released by trypanosomes were identified and, for 12 peptidases, their extracellular delivery was confirmed. Thereafter, the contribution of each peptidase to QS signal production was determined using systematic inducible overexpression in vivo, activity being confirmed to operate through the physiological QS signalling pathway. Gene knockout of the QS-active peptidases identified two enzymes, oligopeptidase B and metallocarboxypeptidase I, that significantly reduced QS when ablated individually. Further, a combinatorial gene knockout of both peptidases confirmed their dominance in the generation of the QS signal, with peptidase release of oligopeptidase B mediated via an unconventional protein secretion pathway. This identifies how the QS signal driving trypanosome virulence and transmission is generated in mammalian hosts. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/472056v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@171e56dorg.highwire.dtl.DTLVardef@8d7ed3org.highwire.dtl.DTLVardef@181885forg.highwire.dtl.DTLVardef@12042e1_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract C_FIG