SERPINB11 is a new noninhibitory intracellular serpin. Common single nucleotide polymorphisms in the scaffold impair conformational change.
SERPINB11, the last of 13 human clade B serpins to be described, gave rise to seven different isoforms. One cDNA contained a premature termination codon, two contained splice variants, and four contained full-length open reading frames punctuated by eight single nucleotide polymorphisms (SNPs). The SNPs encoded amino acid variants located within the serpin scaffold but not the reactive site loop (RSL). Although the mouse orthologue, Serpinb11, could inhibit trypsin-like peptidases, SERPINB11 showed no inhibitory activity. To determine whether the human RSL targeted a different class of peptidases or the serpin scaffold was unable to support inhibitory activity, we synthesized chimeric human and mouse proteins, in which the RSLs had been swapped. The human RSL served as a trypsin inhibitor when supported by mouse scaffold sequences. Conversely, the mouse RSL on the human scaffold showed no inhibitory activity. These findings suggested that variant residues in the SERPINB11 scaffold impaired serpin function. SDS-PAGE analysis supported this notion as RSL-cleaved SERPINB11 was unable to undergo the stressed-to-relaxed transition typical of inhibitory type serpins. Mutagenesis studies supported this hypothesis, since the reversion of amino acid sequences in helices D and I to those conserved in other clade B serpins partially restored the ability of SERPINB11 to form covalent complexes with trypsin. Taken together, these findings suggested that SERPINB11 SNPs encoded amino acids in the scaffold that impaired RSL mobility, and HapMap data showed that the majority of genomes in different human populations harbored these noninhibitory SERPINB11 alleles. Like several other serpin superfamily members, SERPINB11 has lost inhibitory activity and may have evolved a noninhibitory function.
Askew
David J
DJ
University of Pittsburgh Medical Center Newborn Medicine Program, Children's Hospital of Pittsburgh and Magee--Womens Research Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
Cataltepe
Sule
S
Kumar
Vasantha
V
Edwards
Christopher
C
Pace
Serena M
SM
Howarth
Rica N
RN
Pak
Stephen C
SC
Askew
Yuko S
YS
Brömme
Dieter
D
Luke
Cliff J
CJ
Whisstock
James C
JC
Silverman
Gary A
GA
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D020641:Polymorphism, Single Nucleotide; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D015843:Serpins / Q000737:chemistry / Q000502:physiology*; D014018:Tissue Distribution
D011994:Recombinant Proteins; C523319:SERPINB11 protein, human; C523318:SERPINB11 protein, mouse; D015843:Serpins