Signal recognition particle-dependent secretome in humans

About 30% of all cellular proteins are secreted and membrane proteins. They can be transported by signal recognition particle (SRP)-dependent or SRP-independent mechanisms. However, little is known about which proteins are SRP-dependent and SRP-independent in mammals. In this work, we address this fundamental question by mass spectrometry analysis of proteins in cells and conditioned medium when SRP is defective. The analysis demonstrates that the majority of secretory proteins in the medium and many in cells have lower abundance relative to controls, demonstrating the SRP dependence of the human secretome. We also described new SRP-independent proteins. Moreover, we found potential compensatory pathways activated when SRP is defective, and protein network that may play a role in quality control of the secretory and membrane proteins and their mRNAs in humans.