Biology subjects

Buzuk, A.

Publications and source records attributed to Buzuk, A..

6 recordsLinked to original sources

bioRxiv2026

Hierarchical decoding of targeting tripeptide motif by the cytosolic iron-sulfur cluster assembly targeting complex

Iron-sulfur (Fe-S) clusters are essential cofactors required for diverse cellular processes, yet how the Fe-S cluster biogenesis machinery selectively recognizes apo-client proteins remain poorly understood. In eukaryotes, many cytosolic and nuclear Fe-S proteins are recruited to the cytosolic iron-sulfur cluster assembly (CIA) system through a short C-terminal targeting complex recognition (TCR) motif having a [ILM]-[DES]-FW] consensus. Currently, the physicochemical properties underlying this molecular recognition event are undefined. By combining quantitative binding measurements, bioinformatic analysis, and structural modeling, we define the molecular basis for TCR peptide recognition by the CIA targeting complex (CTC). This systematic energetic dissection reveals a hierarchy of binding determinants, in which the side chain and C-terminal carboxylate of the aromatic residue provide the dominant energetic contributor, whereas the upstream residues modulate affinity in a sequence context-dependent manner. Computational docking and molecular dynamics simulations identify an interfacial binding site at the Cia1-Cia2 interface that can accommodate these TCR moieties complementary interaction surfaces. Mutational analysis the identified interaction site is consistent with an aromatic pocket and an adjacent hydrophobic groove on Cia2 accommodating the TCRs terminal aromatic and antepenultimate aliphatic residues. Together, these results reveal the physicochemical decoding grammar by which the CTC recognizes targeting peptides with divergent sequences, illustrating how short targeting motifs can achieve both the specificity and adaptability required for Fe-S protein maturation. Significance StatementIron-sulfur (Fe-S) clusters are essential metallocofactors requiring dedicated pathways for their assembly and insertion into proteins. How Fe-S cluster biogenesis systems selectively recognize their Fe-S binding client proteins in the crowded cellular environment remains poorly understood, in part because these machineries must engage dozens of clients rather than relying on the one-to-one metallochaperone-client pairings commonly used to assemble other types of metalloproteins. In eukaryotes, many cytosolic and nuclear Fe-S proteins are recruited to the cytosolic iron-sulfur assembly (CIA) machinery through a C-terminal targeting tripeptide motif. Here we combine biochemical measurements and structural modeling to define the molecular rules governing recognition of CIA targeting peptides. We show that a hierarchy of physicochemical peptide features, rather than a strict sequence consensus, guides recruitment of clients to the targeting complex, explaining how a single binding site can decode multiple targeting peptide signals.

biochemistry↗

bioRxiv2026

Nar1 binds the cytosolic iron sulfur cluster assembly targeting complex via a bipartite interaction interface

The cytosolic iron-sulfur cluster assembly (CIA) pathway maturates essential nuclear and cytosolic Fe-S proteins required for genome maintenance and cellular metabolism. Nar1 (also called CIAO3 or IOP1) is a conserved Fe-S protein that connects the early and late steps of the CIA pathway, yet the molecular basis for its proposed function as a metallocluster carrier remains poorly defined. In particular, the interactions responsible for Nar1 recruitment to the CIA targeting complex (CTC) during cluster delivery remain unknown. Here, we define the molecular basis for Nar1 recruitment to the CTC using biochemical reconstitution, quantitative protein-protein interaction assays, and AlphaFold modeling. Our data reveal that Nar1 binds the CTC through two distinct interfaces. A primary interface comprises an electrostatic interaction that anchors Nar1 to a conserved acidic surface on the Cia1 subunit of the CTC and a secondary interface involves binding of Nar1s divergent targeting complex recognition peptide at the Cia1-Cia2 interface. Thus, Nar1 engages a conserved CTC surface that serves as a recruitment platform for multiple binding partners, including CIA clients. Computational structural models position the putative Fe-S cluster donor site of Nar1 adjacent to a proposed acceptor site on Cia2, suggesting that this bipartite binding mechanism positions Nar1 for transfer of an Fe-S cluster to the targeting complex. Together, these findings resolve conflicting models for Nar1 recruitment and establish a mechanistic framework for understanding how the CTC engages multiple binding partners during cytosolic iron-sulfur protein maturation.

biochemistry↗

bioRxiv2026

Discovery of a cluster in the PRRSV Nsp1α leader protease reveals host-virus interplay in its downstream functions

Porcine reproductive and respiratory syndrome virus (PRRSV; Betaarterivirus suid) is a major global threat to swine production, yet effective antiviral therapies are lacking. The leader protease Nsp1 is essential for viral replication and innate immune suppression, and its N-terminal zinc-finger (ZF) domain is critical for function, although its molecular role remains unclear. Here, we show that the ZF domain plays only a minor role in protease activity and that Nsp1 is largely inactive following release from the polyprotein. Using Mossbauer and UV/visible spectroscopy combined with chemoproteomics, we demonstrate that the ZF site binds not only Zn but also a [4Fe-4S] cluster. Notably, the Fe-S cluster, but not Zn, allosterically modulates residual protease activity. Nsp1 directly engages the cytosolic iron-sulfur cluster assembly machinery via CIAO1 and competes with the Fe-S carrier CIAO3, establishing the [4Fe-4S] cluster as a bona fide cofactor. These findings redefine Nsp1 as an Fe-S-dependent viral protein and reveal new opportunities for metal-targeted antiviral strategies.

biochemistry↗

bioRxiv2025

The Cia1 and Cia2 subunits of the CTC mediate recognition of apo-FeS proteins with a C-terminal targeting complex recognition motif

The cytosolic iron-sulfur cluster assembly (CIA) targeting complex is responsible for maturation of cytosolic and nuclear iron-sulfur enzymes, numbering >30 proteins critical for fundamental processes such as DNA replication and repair. Up to 25% of these client proteins terminate in a targeting complex recognition (TCR) motif. This carboxy-terminal tripeptide motif recruits the CIA targeting complex (CTC) to the client so that the metallocluster can be inserted. Herein, we use a combination of computational, biochemical and biophysical approaches to determine that the clients bearing a TCR motif docks at the interface of the Cia1 and Cia2 subunits of the CTC. Thus, mutations destabilizing the Cia1-Cia2 complex also disrupt TCR-based client identification by the CTC. Our study also reveals that the understudied human Cia2 paralog CIAO2A, which is proposed to be a specific targeting factor for iron regulatory protein 1, can recruit clients terminating in the TCR peptide. These data signal that CIAO2A plays a more general role in iron-sulfur protein maturation than previously appreciated. Taken together, our findings deepen our understanding of the molecular basis for client recognition by the CTC that is critical to understand the impact of CIA function in human health and disease.

biochemistry↗

bioRxiv2024

Getting Started with Machine Learning for Experimental Biochemists and Other Molecular Scientists

Machine learning (ML) is rapidly gaining traction in many areas of experimental molecular science for elucidating relationships and patterns in large or complex data sets. Historically, ML was largely the preserve of those with specialized training in fields such as statistics or cheminformatics. Increasingly, however, ML methodologies are becoming part of the standard toolkit for experimental scientists across a range of disciplines. Lowering the barrier of entry to these ML techniques, for scientists without a significant background in computer science or statistics, is important to broadening access to these powerful methods. Here we provide detailed, step by step tutorials for performing four ML methods that are particularly useful for applications in biochemistry, cell biology, and drug discovery: hierarchical clustering, Principal Component Analysis (PCA), Partial Least-Squares Discriminant Analysis (PLSDA), and Partial Least-Squares Regression (PLSR). The protocols are written for the widely used software MATLAB, but no prior experience with MATLAB is required to use them. We include an explanation of each step, pitched at a level to be understood by investigators without any prior experience with ML, MATLAB, or any kind of coding. We also highlight the scientific issues pertaining to selecting and scaling the data to be analyzed, and describe controls to test the validity of the results obtained. Throughout, we emphasize the relationship between the scientific question and how to choose data and methods that will allow it to be addressed in a meaningful way. Our aim is to provide a basic introduction that will equip experimental chemical biologists and other chemical and biomedical scientists with the knowledge required to use ML to aid in the design of experiments, the formulation and data-driven testing of hypotheses, and the analysis of experimental data. Basic Protocol 1Clustering Basic Protocol 2Principal Component Analysis (PCA) Basic Protocol 3Partial Least Squares Discriminant Analysis (PLSDA) Basic Protocol 4Partial Least Squares Regression (PLSR)

biochemistry↗

bioRxiv2023

Cytosolic iron-sulfur protein assembly system identifies clients by a C-terminal tripeptide

The eukaryotic cytosolic Fe-S protein assembly (CIA) machinery inserts iron-sulfur (Fe-S) clusters into cytosolic and nuclear proteins. In the final maturation step, the Fe-S cluster is transferred to the apo-proteins by the CIA-targeting complex (CTC). However, the molecular recognition determinants of client proteins are unknown. We show that a conserved [LIM]-[DES]-[WF]-COO- tripeptide present at the C-terminus of clients is necessary and sufficient for binding to the CTC in vitro and directing Fe-S cluster delivery in vivo. Remarkably, fusion of this TCR (target complex recognition) signal enables engineering of cluster maturation on a non-native protein via recruitment of the CIA machinery. Our study significantly advances our understanding of Fe-S protein maturation and paves the way for bioengineering applications. One-Sentence SummaryA C-terminal tripeptide guides eukaryotic iron-sulfur cluster insertion into cytosolic and nuclear proteins.

biochemistry↗