Jameson, G. B. | bioRxiv Science

bioRxiv2023

Structure-guided inhibition of the cancer DNA-mutating enzyme APOBEC3A

The normally antiviral enzyme APOBEC3A1-4 is an endogenous mutagen in many different human cancers5-7, where it becomes hijacked to fuel tumor evolvability. APOBEC3As single-stranded DNA C-to-U editing activity1, 8 results in multiple mutagenic outcomes including signature single-base substitution mutations (isolated and clustered), DNA breakage, and larger-scale chromosomal aberrations5-7. Transgenic expression in mice demonstrates its tumorigenic potential9. APOBEC3A inhibitors may therefore comprise a novel class of anticancer agents that work by blocking mutagenesis, preventing tumor evolvability, and lessening detrimental outcomes such as drug resistance and metastasis. Here we reveal the structural basis of competitive inhibition of wildtype APOBEC3A by hairpin DNA bearing 2-deoxy-5-fluorozebularine in place of the cytidine in the TC recognition motif that is part of a three-nucleotide loop. The nuclease-resistant phosphorothioated derivatives of these inhibitors maintain nanomolar in vitro potency against APOBEC3A, localize to the cell nucleus, and block APOBEC3A activity in human cells. These results combine to suggest roles for these inhibitors to study A3A activity in living cells, potentially as conjuvants, leading toward next-generation, combinatorial anti-mutator and anti-cancer therapies.

cancer biology↗

bioRxiv2019

Interactions in milk suggest a physiological role for β-lactoglobulin

{beta}-Lactoglobulin is the most abundant protein in the whey fraction of ruminant milks, yet is absent in human milk. It has been studied intensively due to its impact on the processing and allergenic properties of ruminant milk products. However, the physiological function of {beta}-lactoglobulin remains unclear. Sedimentation velocity experiments have identified new interactions between fluorescently-labelled {beta}-lactoglobulin and other components in milk. Co-elution experiments support that these {beta}-lactoglobulin interactions occur naturally in milk and provide evidence that the interacting partners are immunoglobulins, while further sedimentation velocity experiments confirm that an interaction occurs between these molecules. Ruminants (e.g. cows and goats) are born without circulating immunoglobulins, which they must obtain from their mothers milk, whilst humans obtain immunoglobulins both through milk and during gestation via the placenta. We propose that {beta}-lactoglobulin serves to protect immunoglobulins within ruminant milk during digestion, ensuring their efficient transfer from mother to offspring.\n\nStatement of Significance{beta}-Lactoglobulin is an abundant protein in the whey fraction of ruminant milks (e.g. cow and goat milk), yet it is completely absent in human milk. While this protein has been extensively studied, due to its impact on the processing and allergenic properties of milk, its physiological function remains unclear. We fluorescently labelled {beta}-lactoglobulin to monitor its interactions with other milk components within its physiological environment, milk. Under these near physiological conditions {beta}-lactoglobulin is capable of interacting with several classes of immunoglobulins. Immunoglobulins are susceptible to digestion, but are required to confer immunity from the mother to the offspring. We propose that {beta}-lactoglobulin serves to protect immunoglobulins within ruminant milk during digestion, ensuring their efficient transfer from mother to offspring.

biophysics↗