Biology subjects

Sandholu, A.

Publications and source records attributed to Sandholu, A..

4 recordsLinked to original sources

bioRxiv2025

Conformation-specific Design: a New Benchmark and Algorithm with Application to Engineer a Constitutively Active MAP Kinase

AO_SCPLOWBSTRACTC_SCPLOWA general method for designing proteins with high conformational specificity is desirable for a variety of applications, including enzyme design and drug target redesign. To assess the ability of algorithms to design for conformational specificity, we introduce MotifDiv, a benchmark dataset of 200 conformational specificity design challenges. We also introduce CSDesign, an algorithm for designing proteins with high preference for a target conformation over an alternate conformation. On the MotifDiv benchmark, CSDesign designs protein sequences that are predicted to prefer the target conformation. We apply this method in vitro to redesign human MAP kinase ERK2, an enzyme with active and inactive conformations. Out of two designs for the active conformation, one increased activity sufficiently to retain activity in the absence of activating phosphorylations, a property not present in the wild type protein.

synthetic biology↗

bioRxiv2025

Plant-specific adaptations of the CDC48 unfoldase

Targeted protein degradation through the CDC48 unfoldase enables the maintenance and rapid adaptation of proteomes across eukaryotes. However, the profound differences between animals, fungi, and plants are expected to have led to a significant adaptation of the CDC48-mediated degradation. While animal and fungal CDC48 systems have shown structural and functional preservation, such analysis is lacking for plants. We determined the structural and functional characteristics of Arabidopsis thaliana CDC48A in various states and bound to the target-identifying cofactors UFD1 and NPL4. Our analysis reveals several features that distinguish AtCDC48 from its animal and yeast counterparts, despite an 80% sequence identity. Key features are that AtCDC48A displays distinct domain dynamics and interacts differently with AtNPL4. Moreover, AtNPL4 and AtUFD1 do not form an obligate heterodimer, but independently bind to AtCDC48A and mediate target degradation; however, their joint action is synergistic. An evolutionary analysis supports that these Arabidopsis features are conserved across plants and represent the ancestral state of eukaryotic CDC48 systems. Jointly, our findings support that plant CDC48 retains a greater modular and combinatorial cofactor usage, highlighting a specific adaptation of targeted protein degradation in plants.

plant biology↗

bioRxiv2024

Functional selection in SH3-mediated activation of the PI3 kinase

The phosphoinositide-3 kinase (PI3K), a heterodimeric enzyme, plays a pivotal role in cellular metabolism and survival. Its deregulation is associated with major human diseases, particularly cancer. The p85 regulatory subunit of PI3K binds to the catalytic p110 subunit via its C-terminal domains, stabilising it in an inhibited state. Certain Src homology 3 (SH3) domains can activate p110 by binding to the proline-rich (PR) 1 motif located at the N-terminus of p85. However, the mechanism by which this N-terminal interaction activates the C-terminally bound p110 remains elusive. Moreover, the intrinsically poor ligand selectivity of SH3 domains raises the question of how they can control PI3K. Combining structural, biophysical, and functional methods, we demonstrate that the answers to both these unknown issues are linked: PI3K-activating SH3 domains engage in additional "tertiary" interactions with the C-terminal domains of p85, thereby relieving their inhibition of p110. SH3 domains lacking these tertiary interactions may still bind to p85 but cannot activate PI3K. Thus, p85 uses a functional selection mechanism that precludes nonspecific activation rather than nonspecific binding. This separation of binding and activation may provide a general mechanism for how biological activities can be controlled by promiscuous protein-protein interaction domains.

biochemistry↗

bioRxiv2023

P-NADs: PUX-based NAnobody Degraders for Ubiquitin-Independent Degradation of Target Proteins

Targeted protein degradation (TPD) allows cells to maintain a functional proteome and to rapidly adapt to changing conditions. Methods that repurpose TPD for the deactivation of specific proteins have demonstrated significant potential in therapeutic and research applications. Most of these methods are based on proteolysis targeting chimaera (PROTAC) which link the protein target to an E3 ubiquitin ligase binding moiety, resulting in the ubiquitin-based degradation of the target protein. In this study, we introduce a method for ubiquitin-independent TPD based on nanobody-conjugated plant ubiquitin regulatory X domain-containing (PUX) adaptor proteins. We show that the PUX-based NAnobody Degraders (P-NADs) can unfold a target protein through the Arabidopsis and human orthologues of the CDC48 unfoldase without the need for ubiquitination or initiating motifs. Despite originating from plants, P-NAD plasmids can be transfected into a human cell line, where produced proteins use the endogenous CDC48 machinery for ubiquitin-independent TPD. Thus, P-NADs pave the road for ubiquitin-independent therapeutic TPD approaches. The P-NAD design combined with established in vitro and cellular assays make this system also a versatile platform for elucidating functional aspects of CDC48-based TPD in plants and animals.

synthetic biology↗