Biology subjects

Balsbaugh, J. L.

Publications and source records attributed to Balsbaugh, J. L..

4 recordsLinked to original sources

bioRxiv2025

APEX2 and TurboID define unique subcellular proteomes

Proximity labeling has emerged as a prominent, reliable tool for obtaining local proteomes from a wide range of cell-types. Two major classes of labeling reagents, peroxidase based (APEX family), or biotin-ligase based (BioID family) have been developed in parallel. These two approaches are often used interchangeably, or chosen based on availability of reagents, however each may produce a biased proteome which should be considered during experimental design. We compared proximity labeling with TurboID or APEX2 in HEK293 cells across cytosol, nucleus, and membrane compartments. Both enzymes enriched compartment-specific proteomes, validated by GO terms, but showed distinct protein profiles. TurboID identified more membrane proteins, favoring identification of proteins associated with RNA processing and protein localization, while APEX2 enriched for proteins involved in metabolic pathways. Trypsin digestion highlighted biases from TurboIDs lysine biotinylation, which we show can be mitigated by an endoproteinase GluC digestion during sample prep, yet these differences persist to some degree. We find that TurboID suits broader proteomic studies whereas APEX2 targets specific signaling pathways. We therefore show that strategic enzyme and protease selection is critical for optimizing proximity labeling-based proteomic studies, advancing cellular proteome mapping.

molecular biology↗

bioRxiv2025

Isoform-specific patterns of phosphorylation on axonemal dynein heavy chains

Axonemal dyneins power ciliary motility and phosphorylation of key intermediate and light chain components affects the regulation and properties of these motors in very distantly related organisms. It is also known that many axonemal dynein heavy chains are subject to this post-translational modification although this has been little studied. Here we examine axonemal dynein heavy chains from a broad range of ciliated eukaryotes and identify phosphorylated sites embedded within various kinase recognition motifs such as those for PKA, PKC and casein kinase II. Mapping these sites onto discrete heavy chain types reveals class-specific locations apparently mediated by different kinases. For example, we find that all Chlamydomonas heavy chain phosphorylation sites are in an extended loop derived from AAA5 that arches over the coiled-coil buttress which in turn interacts with the microtubule-binding stalk. In contrast, most sites in the monomeric inner arm dyneins occur very close to the N-terminus and may be involved in assembly processes. In Chlamydomonas, the two cilia (termed cis and trans) exhibit different intrinsic beat frequencies and we identify cilium-specific phosphorylation patterns on both the heavy chain and outer arm docking complex consistent with differential regulation of these motors in the two organelles. SignificanceO_LIMany axonemal dynein heavy chains are extensively phosphorylated. However, the location, sequence context and potential role of these modifications is uncertain. C_LIO_LIHere we use mass spectrometry to define phosphorylated sites in inner and outer arm dyneins from a broad range of motile ciliated eukaryotes. C_LIO_LIWe identify numerous modified sites that correspond to various kinase consensus sequences and reveal that multiple sites occur in conserved locations depending on dynein heavy chain class. We also find phosphorylation modifications that are specific to either the cis or trans cilium of Chlamydomonas which may be related to their inherent beat frequency imbalance. C_LI

cell biology↗

bioRxiv2023

Proximity labeling reveals new insights into the relationships between meiotic recombination proteins in S. cerevisiae

Several protein ensembles facilitate MutS{gamma} crossover recombination and the associated process of synaptonemal complex (SC) assembly during meiosis, but the physical and functional relationships between the components involved remain obscure. We have employed proximity labeling as a phenotypic tool to discern functional relationships between meiotic recombination and SC proteins in S. cerevisiae, and to gain deeper insight into molecular deficits of crossover-defective mutants. We find that recombination initiation (Spo11) and the Mer3 helicase are dispensable for proximity labeling of the Zip3 E3 ligase by components of the ZZS ensemble (Zip2, Zip4 and Spo16) but are required for proximity labeling of Zip3 by Msh4, consistent with the possibility that MutS{gamma} joins Zip3 only after a specific recombination intermediate has been generated. Proximity labeling analysis of crossover-defective zip1 mutants suggests a key shared defect is a failure to assemble an early recombination ensemble where ZZS can properly engage Zip3. We furthermore discovered that Zip3s abundance within the meiotic cell is uniquely dependent on the presence of Zip1, and that the post-translational modification of Zip3 is promoted by most MutS{gamma} pathway proteins but countered by Zip1. Based on this and additional data, we propose a model whereby Zip1 stabilizes a functional, unmodified form of Zip3 until intermediate steps in recombination are complete. We also find that SC structural protein Ecm11 is proximity labeled by ZZS complex proteins in a Zip4-dependent manner, but by Zip3 and Msh4, at least in part, via a distinct pathway. Finally, streptavidin pulldowns followed by mass spectrometry on eleven different proximity labeling strains uncovers shared proximity targets of MutS{gamma}-associated proteins, some with known meiotic functions and others not yet implicated in a meiotic activity, highlighting the potential power of proximity labeling as a discovery tool.

genetics↗

bioRxiv2021

The Okur-Chung Neurodevelopmental Syndrome (OCNDS) mutation CK2K198R leads to a rewiring of kinase specificity

Okur-Chung Neurodevelopmental Syndrome (OCNDS) is caused by heterozygous mutations to the CSNK2A1 gene, which encodes the alpha subunit of casein kinase II (CK2). The most frequently occurring mutation is lysine 198 to arginine (K198R). To investigate the impact of this mutation, we first generated a high-resolution phosphorylation motif of CK2WT, including the first characterization of specificity for tyrosine phosphorylation activity. A second high resolution motif representing CK2K198R substrate specificity was also generated. Here we report for the first time the impact of the OCNDS associated CK2K198R mutation. Contrary to prior speculation, the mutation does not result in a loss of function, but rather shifts the substrate specificity of the kinase. Broadly speaking the mutation leads to 1) a decreased preference for acidic residues in the +1 position, 2) a decreased preference for threonine phosphorylation, 3) an increased preference for tyrosine phosphorylation, and 4) an alteration of the tyrosine phosphorylation specificity motif. To further investigate the result of this mutation we have developed a probability-based scoring method, allowing us to predict shifts in phosphorylation in the K198R mutant relative to the wild type kinase. As an initial step we have applied the methodology to the set of axonally localized ion channels in an effort to uncover potential alterations of the phosphoproteome associated with the OCNDS disease condition.

neuroscience↗