A protein transduction method for efficiently delivery of exogenous proteins into mammalian cells is invented, which has the capability of targeting different cellular compartments and protection from degradation of the delivered proteins from cellular proteases. A composition for treat proteins has cation reagents, lipids and enhancers in a carrier. The method can be used in a number of ways including: production of large quantities of properly folded, post-translationally modified proteins using mammalian cell machinery, a in-cell fluorescence spectroscopy and imaging using small molecule fluorophores and a in-cell NMR spectroscopy using living mammalian cells. The method permits cell biology at atomic resolution that is physiologically and pathological relevant and permits protein therapy to treat human diseases. The method can also be used to deliver exogenous protein inside mammalian cells, wherein the exogenous proteins follow a similar secretion pathway as that of the endogenous protein.
