Recombinant Escherichia coli Phosphoserine aminotransferase (serC)
Description
Biochemical Function and Structure
SerC (3-phosphoserine aminotransferase) catalyzes the reversible transfer of an amino group between glutamate and 3-phosphohydroxypyruvate (3PHP) to produce 3-phosphoserine and α-ketoglutarate. This reaction is central to the phosphorylated serine biosynthetic pathway, which also intersects with vitamin B6 (pyridoxine) biosynthesis . The enzyme exhibits redundancy and substrate promiscuity, allowing it to participate in multiple metabolic pathways .
Structurally, SerC is a dimer with a subunit molecular weight of ~39,834 Da. Its active site requires pyridoxal 5′-phosphate (PLP) as a cofactor, which facilitates amino group transfer via a pyridoxamine intermediate . Mutational studies have shown that residues R42 and R77 are critical for substrate specificity, with mutations (e.g., R42W/R77W) enhancing activity toward alternative substrates like l-homoserine .
Genetic Regulation and Operon Structure
SerC is encoded by the serC gene, which forms a polycistronic operon with aroA (encoding 5-enolpyruvylshikimate 3-phosphate synthase). This operon is transcribed from a promoter upstream of serC, producing a single mRNA that includes both genes . The operon’s structure allows coordinated regulation of serine and aromatic amino acid biosynthesis, with transcription terminated by a rho-independent terminator downstream of serC .
Key regulatory features include:
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Promoter elements: Consensus -35 (ATGATA) and -10 (TATAATG) sequences, with a 17 bp spacer .
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Transcriptional attenuation: A G+C-rich inverted repeat followed by a poly-T tract facilitates termination of serC expression while allowing aroA transcription to proceed .
Applications in Metabolic Engineering
SerC engineering has been pivotal in optimizing metabolic flux for bioactive compound production:
Role in Genetic Code Expansion
SerC knockout strains (ΔserC) have enabled the incorporation of non-canonical amino acids like phosphoserine (pSer) and its analogs into proteins. Key advancements include:
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Phosphoserine production: Deletion of serC prevents phosphoserine degradation, allowing its accumulation for genetic code expansion (GCE) systems .
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Orthogonal translation systems: Co-expression of phosphoserine biosynthetic pathways and amber-suppressing tRNA systems enables site-specific incorporation of pSer into recombinant proteins .
Production Optimization Strategies
Efficient recombinant SerC production requires tailored approaches:
Product Specs
Target Background
KEGG: ecj:JW0890
STRING: 316385.ECDH10B_0977
