Protein Sequencer

What is the Protein Sequencer?

A protein sequencer determines the N-terminal amino acid sequence of a purified peptide or protein by automated Edman degradation, identifying 20 to 50 residues per run. It is used to confirm protein identity and to characterise N-termini of recombinant products.

Overview

The instrument performs repeated cycles of coupling, cleavage and conversion on a sample immobilised on a glass fibre or PVDF support. Phenylisothiocyanate couples to the free N-terminal amino group, acid cleaves the derivatised residue, and the resulting anilinothiazolinone is converted to a phenylthiohydantoin derivative that is separated by reversed-phase high-performance liquid chromatography and identified by absorbance at 269 nm. Each cycle takes 30–50 minutes, so a 20-residue sequence is generated in about 10–17 hours without intervention. Typical sensitivity is 10–100 pmol of protein, corresponding to a few micrograms. Blocked N-termini, common in recombinant proteins and after formylation or acetylation, prevent sequencing and require deblocking or internal sequence analysis after enzymatic cleavage.

How does it work?

Protein analyzers apply a physical or chemical measurement that responds to a specific property of the molecule. Amino acid analysis hydrolyses the protein and separates the released amino acids by ion exchange or reversed-phase chromatography with ninhydrin or fluorescence detection, giving composition in residues per molecule. Edman degradation removes one amino acid at a time from the N-terminus by phenylisothiocyanate chemistry and identifies each derivative chromatographically, giving the first 20–50 residues. Circular dichroism measures the difference in absorption of left- and right-circularly polarised light, and the far-UV spectrum reports alpha helix, beta sheet and random coil content. Thermal shift assays use a fluorescent dye that reports unfolding as temperature rises, giving a melting temperature that shifts when a ligand binds. Surface plasmon resonance detects mass binding at a sensor surface in real time, yielding association and dissociation rate constants.

What are the key features?

• Automated Edman degradation with 20–50 residues per run
• Reversed-phase HPLC identification of phenylthiohydantoin derivatives
• Sensitivity of 10–100 pmol of purified protein
• PVDF membrane and solution sample support options
• Cycle programs for standard and fast sequencing modes
• Sequence calling software with peak quality review

What are the technical specifications?

A typical protein sequencer configuration offers residues per run of 20–50 (sample dependent), sensitivity of approx. 10–100 pmol, cycle time of approx. 30–50 min per residue, initial yield of approx. 50–90% (typical), repetitive yield of approx. 90–95% per cycle and detection of UV absorbance at 269 nm. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Protein Sequencer is used in N-terminal identity confirmation of recombinant proteins, peptide and fragment sequence verification, quality control of synthetic peptides and characterisation of purified native proteins. Across the wider Protein Analyzers class, laboratories also deploy it for recombinant protein characterisation, biosimilar comparability studies and protein structure and folding research.

Which standards and certifications apply?

Relevant standards and methods include USP <1057>, Ph. Eur. 2.2.56, Ph. Eur. 2.2.25, ISO 17025, IEC 61010-1 and 21 CFR Part 11. Certification candidates for this model are CE, ISO 9001 manufacturing and IEC 61010-1 safety; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Sample purity and buffer composition dominate results, so prepare proteins in volatile, low-absorbing buffers for circular dichroism and avoid detergents and reducing agents that absorb in the far UV. Amino acid analysis needs complete hydrolysis, so ampoule sealing, vacuum and hydrolysis time must be controlled. Surface plasmon resonance sensors are sensitive to buffer refractive index differences, so running buffer and sample buffer should match and a reference channel should be included. Thermal shift assays need consistent dye concentration and controlled heating rates. Verify performance periodically with a reference protein such as bovine serum albumin or lysozyme, keep maintenance and calibration records, and store raw data, since circular dichroism and biosensor results are often re-analysed after method changes.

How do I select the right Protein Sequencer?

Select a protein sequencer when N-terminal sequence data are required for identity or release testing and mass spectrometry cannot resolve the question. Specify sensitivity, cycle time, sequencing mode options and sample support format, and confirm that the software exports raw chromatograms for review.

How does it compare with other Protein Analyzers variants?

Choose the analyzer that measures the property you must document. For composition or identity of a purified protein, amino acid analysis gives a quantitative profile; Edman sequencing provides N-terminal sequence but needs a pure, unblocked sample. Circular dichroism is the standard method for secondary structure comparison between batches and for folding studies, and it needs only 0.2–0.5 mg/mL in a low-absorbing buffer. Thermal shift assays screen buffer conditions and ligand binding quickly in 96-well format, making them useful early in development. Surface plasmon resonance quantifies affinity and kinetics, and it demands careful immobilisation chemistry and reference channel design. Compare sample consumption, sensitivity, throughput, buffer tolerance, temperature control and whether the software can export raw traces for independent analysis.