SOMAmer reagents are selected using the SELEX (Systematic Evolution of Ligands using Exponential Enrichment) method, starting with libraries of 1015 molecules and iteratively narrowing that number based on affinity of the rounds of SELEX. Usually about 100 sequences are available after 6 – 8 rounds of SELEX that have acceptable affinity to the target. While all of the SOMAmer reagent candidates will bind the target to varying degrees, the properties of these reagents will vary, including their performance in any given application. While one sequence might perform well in one set of conditions, another sequence may perform better in another.
Are there preferred sources of target protein (e.g. recombinant systems, etc.)?
SOMAmers recognize the tertiary structure of proteins, so protein sources that create a properly folded protein are preferred.
Can a custom SOMAmer reagent be designed to discriminate between protein variants or post- translational modifications (PTMs) of the target protein?
SOMAmer reagents that discriminate between protein variants (e.g. highly homologous proteins or mutant forms of the same protein) have been successfully discovered at SomaLogic. Because SOMAmer reagents bind large, conformational epitopes it is difficult to predict ahead of time the chance for success; however there are several examples where this has been achieved with high specificity. Please contact SomaLogic Technical Support at techsupport@somalogic.com or by telephone at 1-800- 324-0783 or 303-625-9000 regarding any specific concerns.
How many libraries are used to identify candidate SOMAmer reagents that bind to the target analyte?
SomaLogic will use up to two differentially modified DNA libraries in the SELEX process to identify SOMAmer reagents that bind the analyte target. Additional libraries are available for an additional fee. Please contact your sales representative or at orders@somalogic.com for additional information.
How many SOMAmer binding reagents will be obtained during the custom SOMAmer Discovery Service process?
During the standard process for custom SOMAmer design, we will provide at least 5 nmoles each of 5 candidate SOMAmer binding reagents with Kd values of less than 25 nM (or all candidates meeting this dissociation standard if fewer than 5 are discovered) to the customer for orthogonal testing/validation. Upon selection of one of these SOMAmer reagents by the customer, a single fit-for- purpose SOMAmer reagent will be provided at 50 nmoles. Additional SOMAmer reagents may be purchased at this time for an additional cost; please contact SomaLogic Sales at orders@somalogic.com or by telephone at 1-844-SOMAMER (1-844-766-2637) or the main number at 303-625-9000.
How much target protein is required to design a custom SOMAmer reagent?
For standard SOMAmer Discovery Service projects, we request that a minimum of 250 μg of purified protein (in the native, folded form) be submitted. If less than this amount is available, please contact SomaLogic Sales at orders@somalogic.com or by telephone at 1-844-SOMAMER (1-844-766-2637) or the main number at 303-625-9000. For projects that entail custom processes, more protein may be requested.
What are acceptable fusion tags on the target analyte?
In general, fusion tags such as polyHis, human IgG1 Fc, and biotin are acceptable. GST and HALO tags are incompatible with the SOMAmer Discovery Service at this time. Please contact SomaLogic Technical Support at techsupport@somalogic.com or by telephone at 1-800-324-0783 or 303-625-9000 regarding other fusion tags of interest.
What are the expected dissociation constants (Kd) for the candidate SOMAmer binding reagents?
SomaLogic will provide at least 5 nmoles each of 5 candidate SOMAmer binding reagents with Kd values of less than 25 nM, or all candidates meeting this dissociation standard if fewer than 5 are discovered. The median affinity for the SOMAmer reagents in SomaLogic’s biomarker discovery assay is 0.9 nM.
What buffers are compatible with the SOMAmer Discovery process (i.e. in what buffers can the target analyte be suspended)?
In general, mild non-denaturing buffers are compatible with the process as long as they do not have an extreme pH (e.g. pH<4 or pH>10) or high detergent content. Denaturing buffers are incompatible with the SOMAmer Discovery Service at this time. Please contact SomaLogic Technical Support at techsupport@somalogic.com or by telephone at 1-800-324-0783 or 303-625-9000 regarding any specific buffer concerns.
What is the minimum size protein target that can be used when designing a custom SOMAmer reagent?

The target protein should be a minimum of 25 amino acids excluding fusion tags (e.g. polyHis, IgG, biotin, etc.). If the target protein of interest is less than 25 amino acids, it may be possible to design a custom SOMAmer reagent, but please contact SomaLogic Technical Support at techsupport@somalogic.com or by telephone at 1-800-324-0783 or 303-625-9000.

Will the epitope on the target analyte be known?

Crystal structure analyses of a small number of SOMAmer reagent-protein complexes indicate SOMAmer reagents bind large, conformational epitopes, but the exact epitope of every SOMAmer reagent is not known.