Role of Interfacial Morphology in Cu2O/TiO2 and Band Bending: Insights from Density Functional Theory.

Photocatalysis, a promising solution to environmental challenges, relies on the generation and utilization of photogenerated charge carriers within photocatalysts. However, the recombination of these carriers often limits efficiency. Heterostructures, especially Cu2O/TiO2, have emerged as effective solutions to enhance charge separation. This study systematically explores the effect of interfacial morphologies on the band bending within Cu2O/TiO2 anatase heterostructures by employing density functional theory. Through this study, eight distinct interfaces are identified and analyzed, revealing a consistent staggered-type band alignment. Despite variations in band edge positions, systematic charge transfer from Cu2O to TiO2 is observed across all interfaces. The proposed band bending configurations would suggest enhanced charge separation and photocatalytic activity under ultraviolet illumination due to a Z-scheme configuration. This theoretical investigation provides valuable insights into the interplay between interfacial morphology, band bending, and charge transfer for advancing the understanding of fundamental electronic mechanisms in heterostructures.

Nuclear localization signal sequence is required for VACM-1/CUL5-dependent regulation of cellular growth.

VACM-1/CUL5 is a member of the cullin family of proteins involved in the E3 ligase-dependent degradation of diverse proteins that regulate cellular proliferation. The ability of VACM-1/CUL5 to inhibit cellular growth is affected by its posttranslational modifications and its localization to the nucleus. Since the mechanism of VACM-1/CUL5 translocation to the nucleus is not clear, the goal of this project was to determine the role that the putative nuclear localization signal (NLS) we identified in the VACM-1/CUL5 (640PKLKRQ646) plays in the cellular localization of VACM-1/CUL5 and its effect on cellular growth. We used site-directed mutagenesis to change Lys642 and Lys644 to Gly and the mutated cDNA constructs were transfected into COS-1 cells. Mutation of the NLS in VACM-1/CUL5 significantly reduced its localization to the nucleus and compromised its effect on cellular growth. We have shown previously that the antiproliferative effect of VACM-1/CUL5 could be reversed by mutation of PKA-specific phosphorylation sequence (S730AVACM-1/CUL5), which was associated with its increased nuclear localization and modification by NEDD8. Thus, we examined whether these properties can be controlled by the NLS. The mutation of NLS in S730AVACM-1/CUL5 cDNA compromised its proliferative effect and reduced its localization to the nucleus. The immunocytochemistry results showed that, in cells transfected with the mutant cDNAs, the nuclear NEDD8 signal was decreased. Western blot analysis of total cell lysates, however, showed that VACM-1/CUL5 neddylation was not affected. Together, these results suggest that the presence of the NLS, both in VACM-1/CUL5 and in S730AVACM-1/CUL5 sequences, is critical for their control of cell proliferation.

Mutational analysis of VACM-1/cul5 exons in cancer cell lines.

VACM-1, a cul-5 gene product, functions via an E3 ligase complex and when overexpressed, has an antiproliferative effect in many cell types. Overexpression of VACM-/cul5 cDNA mutated at the PKA-specific phosphorylation site at Ser730 reversed this phenotype. These effects are associated with the appearance of larger M(r) species subsequently identified as a Nedd8-modified VACM-1/cul5. Although decreased levels of VACM-1 mRNA detected in several cancers and cancer cell lines may explain the progression of cell growth, possible genetic and epigenetic changes in its sequence have not been analyzed. We hypothesized that in rapidly proliferating cells, VACM-1/cul5 may be mutated at either the PKA-specific phosphorylation site or the consensus neddylation site. We used RT-PCR and PCR, to amplify and to sequence mRNA and genomic DNA, respectively. To date we have sequenced all 19 coding exons of the VACM-1/cul5 gene in T47D breast cancer cells, U138MG glioma cells, ACHN renal cancer cells, and OVCAR-3 ovarian cancer cells. Our results indicate that in those cells VACM-1/cul5 is not mutated at the putative phosphorylation or the neddylation site. We have found one silent mutation in the genomic DNA isolated from U138MG, ACHN, and OVCAR-3 cell lines, but not from T47D cells. Our work suggests that in T47D breast cancer cells biologic activity of VACM-1/cul5 may be regulated by posttranslational modifications.