Identification and structural influence of a differentially modified N-terminal methionine in human S100b.
The calcium-binding protein S100b is a homodimer comprised of two identical 91-residue beta-subunits. Recombinant S100b is a heterogeneous protein, although the basis of this heterogeneity has not been established. We have used mass spectrometry and NMR spectroscopy to determine that heterogeneity in S100b arises from a mixture of formyl-S100b and desformyl-S100b when expressed in Escherichia coli. Reversed-phase HPLC purification of these two forms of S100b has allowed the differences in N-terminal composition to be used as a probe for tertiary contacts in the protein. The presence or absence of the N-terminal formyl group affected the chemical shifts of sequence neighboring residues and those in the linker of the protein (residues 40-43), indicating that these two regions are close in space.
Smith
S P
SP
Department of Biochemistry, University of Western Ontario, London, Canada.
Barber
K R
KR
Shaw
G S
GS
D000595:Amino Acid Sequence; D002135:Calcium-Binding Proteins / Q000737:chemistry; D006801:Humans; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008715:Methionine; D009414:Nerve Growth Factors; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins / Q000737:chemistry*
D002135:Calcium-Binding Proteins; D046911:Macromolecular Substances; D009414:Nerve Growth Factors; D011994:Recombinant Proteins; D064568:S100 Calcium Binding Protein beta Subunit; D009418:S100 Proteins; C579160:S100B protein, human; D008715:Methionine