Development of phospho-specific Rab protein antibodies to monitor in vivo activity of the LRRK2 Parkinson's disease kinase.

Mutations that activate the LRRK2 (leucine-rich repeat protein kinase 2) protein kinase predispose to Parkinson's disease, suggesting that LRRK2 inhibitors might have therapeutic benefit. Recent work has revealed that LRRK2 phosphorylates a subgroup of 14 Rab proteins, including Rab10, at a specific residue located at the centre of its effector-binding switch-II motif. In the present study, we analyse the selectivity and sensitivity of polyclonal and monoclonal phospho-specific antibodies raised against nine different LRRK2-phosphorylated Rab proteins (Rab3A/3B/3C/3D, Rab5A/5B/5C, Rab8A/8B, Rab10, Rab12, Rab29[T71], Rab29[S72], Rab35 and Rab43). We identify rabbit monoclonal phospho-specific antibodies (MJFF-pRAB10) that are exquisitely selective for LRRK2-phosphorylated Rab10, detecting endogenous phosphorylated Rab10 in all analysed cell lines and tissues, including human brain cingulate cortex. We demonstrate that the MJFF-pRAB10 antibodies can be deployed to assess enhanced Rab10 phosphorylation resulting from pathogenic (R1441C/G or G2019S) LRRK2 knock-in mutations as well as the impact of LRRK2 inhibitor treatment. We also identify rabbit monoclonal antibodies displaying broad specificity (MJFF-pRAB8) that can be utilised to assess LRRK2-controlled phosphorylation of a range of endogenous Rab proteins, including Rab8A, Rab10 and Rab35. The antibodies described in the present study will help with the assessment of LRRK2 activity and examination of which Rab proteins are phosphorylated in vivo These antibodies could also be used to assess the impact of LRRK2 inhibitors in future clinical trials.

Antibody Production with Synthetic Peptides.

Peptides (usually 10-20 amino acid residues in length) can be used as effectively as proteins in raising antibodies producing both polyclonal and monoclonal antibodies routinely with titers higher than 20,000. Peptide antigens do not function as immunogens unless they are conjugated to proteins. Production of high quality antipeptide antibodies is dependent upon peptide sequence selection, the success of peptide synthesis, peptide-carrier protein conjugation, the humoral immune response in the host animal, the adjuvant used, the peptide dose administered, the injection method, and the purification of the antibody. Peptide sequence selection is probably the most critical step in the production of antipeptide antibodies. Although the process for designing peptide antigens is not exact, several guidelines and computational B-cell epitope prediction methods can help maximize the likelihood of producing antipeptide antibodies that recognize the protein. Antibodies raised by peptides have become essential tools in life science research. Virtually all phospho-specific antibodies are now produced using phosphopeptides as antigens. Typically, 5-20 mg of peptide is enough for antipeptide antibody production. It takes 3 months to produce a polyclonal antipeptide antibody in rabbits that yields ~100 mL of serum which corresponds to ~8-10 mg of the specific antibody after affinity purification using a peptide column.

Nature-inspired design of motif-specific antibody scaffolds.

Aberrant changes in post-translational modifications (PTMs) such as phosphate groups underlie a majority of human diseases. However, detection and quantification of PTMs for diagnostic or biomarker applications often require PTM-specific monoclonal antibodies (mAbs), which are challenging to generate using traditional antibody-selection methods. Here we outline a general strategy for producing synthetic, PTM-specific mAbs by engineering a motif-specific 'hot spot' into an antibody scaffold. Inspired by a natural phosphate-binding motif, we designed and selected mAb scaffolds with hot spots specific for phosphoserine, phosphothreonine or phosphotyrosine. Crystal structures of the phospho-specific mAbs revealed two distinct modes of phosphoresidue recognition. Our data suggest that each hot spot functions independently of the surrounding scaffold, as phage display antibody libraries using these scaffolds yielded >50 phospho- and target-specific mAbs against 70% of target peptides. Our motif-specific scaffold strategy may provide a general solution for rapid, robust development of anti-PTM mAbs for signaling, diagnostic and therapeutic applications.

Serine 62 is a phosphorylation site in folliculin, the Birt-Hogg-Dubé gene product.

Recently, it was reported that the product of Birt-Hogg-Dubé syndrome gene (folliculin, FLCN) is directly phosphorylated by 5'-AMP-activated protein kinase (AMPK). In this study, we identified serine 62 (Ser62) as a phosphorylation site in FLCN and generated an anti-phospho-Ser62-FLCN antibody. Our analysis suggests that Ser62 phosphorylation is indirectly up-regulated by AMPK and that another residue is directly phosphorylated by AMPK. By binding with FLCN-interacting proteins (FNIP1 and FNIP2/FNIPL), Ser62 phosphorylation is increased. A phospho-mimic mutation at Ser62 enhanced the formation of the FLCN-AMPK complex. These results suggest that function(s) of FLCN-AMPK-FNIP complex is regulated by Ser62 phosphorylation.

Generation and characterization of a novel phospho-specific monoclonal antibody to p120-catenin serine 879.

To better understand the mechanisms that regulate p120-catenin (p120) and E-cadherin function, we are systematically generating phospho-specific monoclonal antibodies (MAb) to the major p120 phosphorylation sites. p120 has emerged recently as a master regulator of E-cadherin stability and an important modulator of RhoGTPase activities. A number of phosphorylation sites have been identified, but none have as yet been linked to specific regulatory roles. Here, we describe a novel phospho-specific monoclonal antibody to the major PKC-induced p120 phosphorylation site, phospho-serine 879 (pS879). With a few exceptions, p120 MAb pS879 is remarkably specific for the phosphorylated S879 epitope and works effectively in common applications such as Western blot analysis, immunoprecipitation, and immunofluorescence. p120 MAb pS879 should facilitate efforts to identify the role of S879 phosphorylation and to map signaling pathways that modify p120 function through activation of PKC.

Generation and utilization of phosphorylation state-specific antibodies to investigate signaling pathways.

Phosphorylation state-specific antibodies can be of great use, for example, in studying individual steps within a given signal transduction pathway. This unit presents a general approach to the generation and purification of phosphorylation state-specific antibodies. In addition to their ability to detect phosphorylation at a particular key site, these antibodies are often more sensitive for biochemical studies. Besides their application in immunoblotting procedures, activation state-specific antibodies can be used as immunohistochemical reagents. Thus, critical changes in phosphorylation can be monitored as described on an individual cell basis or in fixed tissue sections. Such antibodies can be used to address fundamental questions about signal transduction pathways during physiologic events that cannot be resolved by more conventional methodologies.