RESUMO
We have isolated mutations in the major coat protein P8 of M13 phage that greatly increase the surface display of monomeric or oligomeric proteins. The monomeric protein, human growth hormone (hGH), was fused to the N terminus of P8; libraries of P8 variants were constructed and variants that increased hGH display were selected by binding to the extracellular domain of the hGH receptor. The hGH-P8 fusion protein was found to be extremely tolerant of mutations, and a number of P8 variants were found that increased display to levels that improved detection of the hGH-P8 fusion by almost 100-fold. The increased display likely results from better accommodation of the hGH-P8 fusion protein in the phage coat. Using this high copy display format, it was possible for the first time to detect variants of hGH with very weak affinities for the hGHbp (K(d)>1 microM). The display of a tetrameric protein, streptavidin (approximately 50 kDa), was also increased, suggesting the approach may be general to many proteins. The initial product of a natural or invented selection from a naive library is often a weakly functioning protein. These improvements in high copy display should facilitate the broader goal for selection of proteins with novel functions.
Assuntos
Avaliação Pré-Clínica de Medicamentos/métodos , Expressão Gênica , Biblioteca de Peptídeos , Proteínas/química , Proteínas/metabolismo , Sequência de Aminoácidos , Bacteriófago M13/genética , Bacteriófago M13/metabolismo , Bacteriófago M13/fisiologia , Sequência de Bases , Capsídeo/genética , Capsídeo/metabolismo , Ensaio de Imunoadsorção Enzimática , Variação Genética/genética , Hormônio do Crescimento Humano/química , Hormônio do Crescimento Humano/genética , Hormônio do Crescimento Humano/metabolismo , Humanos , Soros Imunes/imunologia , Modelos Moleculares , Dados de Sequência Molecular , Peso Molecular , Mutação/genética , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Ligação Proteica , Proteínas/genética , Receptores da Somatotropina/química , Receptores da Somatotropina/metabolismo , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Estreptavidina/química , Estreptavidina/genética , Estreptavidina/imunologia , TermodinâmicaRESUMO
Stimulation of GH receptors leads to rapid activation of Jak2 kinase and subsequent tyrosine phosphorylation of the GH receptor. Three specific tyrosines located in the C-terminal domain of the GH receptor have been identified as being involved in GH-stimulated transcription of the Spi 2.1 promoter. Mutated GH receptors lacking all but one of these three tyrosines are able to mediate a transcriptional response when transiently transfected into CHO cells together with a Spi 2.1 promoter/luciferase construct. Similarly, these GH receptors were found to be able to mediate activation of Stat5 DNA-binding activity, whereas the GH receptor mutant lacking all intracellular tyrosines was not. Synthetic tyrosine phosphorylated peptides corresponding to the GH receptor sequence around the three tyrosines inhibited Stat5 DNA-binding activity while their non-phosphorylated counterparts were ineffective. Tyrosine phosphorylated GST-GH receptor fusion proteins specifically bound to Stat5 in extracts from COS 7 cells transfected with Stat5 cDNA. This binding could be inhibited by tyrosine phosphorylated peptides derived from the GH receptor. This study thus demonstrated that specific GH receptor tyrosine residues, in their phosphorylated state, are involved in transcriptional signaling by directly interacting with Stat5.