RESUMO
De novo protein design has enabled the creation of new protein structures. However, the design of functional proteins has proved challenging, in part due to the difficulty of transplanting structurally complex functional sites to available protein structures. Here, we used a bottom-up approach to build de novo proteins tailored to accommodate structurally complex functional motifs. We applied the bottom-up strategy to successfully design five folds for four distinct binding motifs, including a bifunctionalized protein with two motifs. Crystal structures confirmed the atomic-level accuracy of the computational designs. These de novo proteins were functional as components of biosensors to monitor antibody responses and as orthogonal ligands to modulate synthetic signaling receptors in engineered mammalian cells. Our work demonstrates the potential of bottom-up approaches to accommodate complex structural motifs, which will be essential to endow de novo proteins with elaborate biochemical functions, such as molecular recognition or catalysis.
Assuntos
Engenharia de Proteínas/métodos , Motivos de Aminoácidos/genética , Sítios de Ligação/genética , Catálise , Ligantes , Modelos Moleculares , Ligação Proteica/genética , Dobramento de Proteína , Proteínas/químicaRESUMO
O-Acetylation of the capsular polysaccharide (CPS) of Neisseria meningitidis serogroup A (NmA) is critical for the induction of functional immune responses, making this modification mandatory for CPS-based anti-NmA vaccines. Using comprehensive NMR studies, we demonstrate that O-acetylation stabilizes the labile anomeric phosphodiester-linkages of the NmA-CPS and occurs in position C3 and C4 of the N-acetylmannosamine units due to enzymatic transfer and non-enzymatic ester migration, respectively. To shed light on the enzymatic transfer mechanism, we solved the crystal structure of the capsule O-acetyltransferase CsaC in its apo and acceptor-bound form and of the CsaC-H228A mutant as trapped acetyl-enzyme adduct in complex with CoA. Together with the results of a comprehensive mutagenesis study, the reported structures explain the strict regioselectivity of CsaC and provide insight into the catalytic mechanism, which relies on an unexpected Gln-extension of a classical Ser-His-Asp triad, embedded in an α/ß-hydrolase fold.
Assuntos
Cápsulas Bacterianas/química , Cápsulas Bacterianas/metabolismo , Neisseria meningitidis Sorogrupo A/metabolismo , Polissacarídeos Bacterianos/química , Polissacarídeos Bacterianos/metabolismo , Acetilação , Acetiltransferases , Anticorpos Antibacterianos , Cápsulas Bacterianas/genética , Cápsulas Bacterianas/imunologia , Vacinas Bacterianas/imunologia , Hexosaminas , Modelos Moleculares , Neisseria meningitidis Sorogrupo A/genética , Polissacarídeos Bacterianos/genética , Polissacarídeos Bacterianos/imunologia , Conformação ProteicaRESUMO
De novo protein design has been successful in expanding the natural protein repertoire. However, most de novo proteins lack biological function, presenting a major methodological challenge. In vaccinology, the induction of precise antibody responses remains a cornerstone for next-generation vaccines. Here, we present a protein design algorithm called TopoBuilder, with which we engineered epitope-focused immunogens displaying complex structural motifs. In both mice and nonhuman primates, cocktails of three de novo-designed immunogens induced robust neutralizing responses against the respiratory syncytial virus. Furthermore, the immunogens refocused preexisting antibody responses toward defined neutralization epitopes. Overall, our design approach opens the possibility of targeting specific epitopes for the development of vaccines and therapeutic antibodies and, more generally, will be applicable to the design of de novo proteins displaying complex functional motifs.
