The proteome as a whole: from a passive reflection of the transcriptome to an active cellular organizer

Despite advances in proteomics, the proteome is still often viewed as a passive reflection of the transcriptome. Using Mycoplasma gallisepticum as a minimal cell model, we analyzed large-scale datasets across multiple stress conditions to investigate whether the proteome functions as an integrated regulatory system. The proteome remained quantitatively stable under stress, yet the bacteria adapted successfully. We identified a minimal core of 17 major proteins constituting 35% of cellular protein mass. These proteins exhibit distinct physicochemical properties--higher positive charge, lower hydrophilicity, and enrichment in intrinsically disordered regions--suggesting they shape cytoplasmic organization and may drive liquid-liquid phase separation. Minor proteins form tightly correlated clusters, while stress conditions trigger rearrangement of protein complexes without abundance changes, representing an energy-efficient adaptation strategy. Cross linking mass spectrometry revealed condition specific interactome remodeling, which may underlie mycoplasma adaptation to diverse stresses. Our findings suggest that the proteome operates as an active cellular organizer, where physicochemical properties and dynamic complex rearrangements enable adaptation independently of transcriptional control. This framework may inform synthetic biology efforts to engineer minimal cells.