Final answer:
Scientists overexpress low-abundance proteins using strong promoters in a host organism, followed by purification with chromatographic techniques and mass spectrometry for analysis and structural studies.
Step-by-step explanation:
To purify and study proteins that are naturally expressed at low levels, scientists typically use a combination of techniques to overexpress the proteins in a more manageable system, such as bacteria, yeast, or mammalian cells, before purifying them.
One common method is to clone the gene that encodes for the protein of interest into a plasmid with a strong promoter to drive high levels of transcription in a host organism. The protein can then be purified using various chromatographic techniques, such as affinity chromatography, which can include tags that bind specifically to certain resins or antibodies. This is followed by additional purification steps like ion-exchange chromatography, size-exclusion chromatography, and sometimes even more advanced methods if the protein is particularly stubborn. In situations where standard overexpression and purification methods result in low yields or inactive proteins, alternative techniques like cell-free protein synthesis, using systems derived from E. coli as described by Nirenberg and Matthaei may be employed. Furthermore, proteins that are particularly low in abundance may be concentrated using fractionation techniques like polyethylene glycol (PEG) fractionation before analysis. Finally, the proteins are typically identified and their characteristics are analyzed using mass spectrometry or other techniques like X-ray crystallography or nuclear magnetic resonance (NMR) spectroscopy.