RESUMO
The base excision repair (BER) pathway repairs oxidized lesions in the DNA that result from reactive oxygen species generated in cells. If left unrepaired, these damaged DNA bases can disrupt cellular processes such as replication. NEIL1 is one of the 11 human DNA glycosylases that catalyze the first step of the BER pathway, i.e. recognition and excision of DNA lesions. NEIL1 interacts with essential replication proteins such as the ring-shaped homotrimeric proliferating cellular nuclear antigen (PCNA). We isolated a complex formed between NEIL1 and PCNA (±DNA) using size exclusion chromatography (SEC). This interaction was confirmed using native gel electrophoresis and mass spectrometry. Stokes radii measured by SEC hinted that PCNA in complex with NEIL1 (±DNA) was no longer a trimer. Height measurements and images obtained by atomic force microscopy also demonstrated the dissociation of the PCNA homotrimer in the presence of NEIL1 and DNA, while small-angle X-ray scattering analysis confirmed the NEIL1 mediated PCNA trimer dissociation and formation of a 1:1:1 NEIL1-DNA-PCNA(monomer) complex. Furthermore, ab initio shape reconstruction provides insights into the solution structure of this previously unreported complex. Together, these data point to a potential mechanistic switch between replication and BER.
Assuntos
DNA Glicosilases/metabolismo , Antígeno Nuclear de Célula em Proliferação/metabolismo , DNA/química , DNA/metabolismo , DNA Glicosilases/química , Humanos , Microscopia de Força Atômica , Antígeno Nuclear de Célula em Proliferação/química , Antígeno Nuclear de Célula em Proliferação/ultraestrutura , Espalhamento a Baixo Ângulo , Difração de Raios XRESUMO
Leptin plays a central role in the control of body weight and energy homeostasis, but is a pleiotropic cytokine with activities on many peripheral cell types. In this review, we discuss the interaction of leptin with its receptor, and focus on the structural and mechanistic aspects of the extracellular aspects of leptin receptor (LR) activation. We provide an extensive overview of all structural information that has been obtained for leptin and its receptor via X-ray crystallography, electron microscopy, small-angle X-ray scattering, homology modeling, and mutagenesis studies. The available knowledge is integrated into putative models toward a recapitulation of the LR activation mechanism.
Assuntos
Leptina/química , Estrutura Terciária de Proteína , Receptores para Leptina/química , Transdução de Sinais , Sequência de Aminoácidos , Humanos , Leptina/genética , Leptina/metabolismo , Modelos Moleculares , Dados de Sequência Molecular , Ligação Proteica , Receptores para Leptina/genética , Receptores para Leptina/metabolismo , Homologia de Sequência de AminoácidosRESUMO
Leptin activates its cognate receptor (LR) to regulate body weight and metabolically costly processes, such as reproduction and immune responses. Despite such benevolent pleiotropy, leptin-mediated signaling has been implicated in autoimmune diseases and breast cancer, thereby rejuvenating interest in leptin antagonism. We present comparative biochemical and structural studies of the LR ectodomain (LRecto) in complex with wild-type and antagonist leptin variants. We show that high-affinity binding of leptin to the cytokine receptor homology 2 domain of LRecto primes interactions with the Ig-domain (LRIg) of another leptin-bound LRecto to establish a quaternary assembly. In contrast, antagonist leptin variants carrying mutations at the LRIg binding site only enable binary complexes with LRecto. Acetylation of free cysteines in LRecto also abrogates quaternary complexes, suggesting a functional role for intrareceptor disulfides. We propose a revised conceptual framework for LR activation whereby leptin activates predimerized LR at the cell surface to seed higher order complexes with 4:4 stoichiometry.