Protein Analysis FAQ

• • Why Do Two Samples Differ in CD but Not in UV Spectra (P > 0.05)? Which Result Is More Reliable?

  When interpreting discrepancies between circular dichroism (CD) and ultraviolet (UV) spectroscopy results, it is important to consider the type of structural information each technique provides as well as their respective sensitivities. The following explains in detail the possible causes of such discrepancies and offers guidance on how to interpret the results appropriately:   Circular Dichroism (CD) vs. Ultraviolet (UV) Spectroscopy 1. Circular Dichroism (CD) (1) Far-UV CD (190–250 nm): Primarily us......

• • Why Does SUMO-Tagged Protein Fail to Undergo On-Column Cleavage on a Nickel Affinity Column?

  This issue may arise due to several contributing factors:   Insufficient Enzyme Activity The protease used for cleavage may exhibit low activity or may have lost its activity entirely. Enzyme performance can be affected by various factors such as storage conditions, temperature, and pH. It is recommended to verify the enzyme’s quality and storage conditions, or to use freshly prepared enzyme stocks.   Inadequate Enzyme Concentration The amount of enzyme added may be insufficient to ensure efficient in......

• • What Are the Methods for Deglycosylating Glycoproteins?

  Deglycosylation of glycoproteins refers to the process of removing carbohydrate moieties from glycoprotein molecules. Several established methods are commonly employed in laboratory settings to achieve this, broadly categorized into enzymatic and chemical approaches:   Enzymatic Deglycosylation 1. Endoglycosidases Enzymes such as PNGase F are widely used for cleaving most N-linked glycans from glycoproteins with high specificity and efficiency.   2. Exoglycosidases Enzymes like sialidases (also known ......

• • What Are the Detailed Experimental Procedures for Glycosylation Analysis?

  The experimental workflow for glycosylation analysis can vary significantly depending on the specific analytical goals and selected methodologies. Mass spectrometry (MS) is a powerful tool capable of providing in-depth information regarding glycosylation sites and glycan structures. Here, we present a representative protocol for the analysis of protein N-glycosylation using MS-based techniques:   Sample Preparation 1. Protein Extraction Total proteins are extracted from biological samples such as cell......

• • What Are the Common Post-Translational Modifications of Proteins? Provide Four Examples

  Post-translational modifications (PTMs) are covalent modifications that occur after a protein has been synthesized from mRNA into a polypeptide chain. These modifications play a crucial role in determining protein function, activity, stability, and subcellular localization. The following are four representative types of post-translational modifications: 1. Phosphorylation Phosphorylation is a pivotal post-translational modification that involves the covalent attachment of a phosphate group (PO₄³⁻) to ......

• • How to Use Chromatography to Purify Enzymes and Determine the Target Protein

  Sample preparation: The cells or tissues containing the target enzyme are lysed to obtain the crude cell extract. Ultrasonication, high-pressure homogenization, or other methods are commonly used to lyse the cells. Centrifugation is used to remove cell debris and unbroken cells after lysis. Preliminary purification: Fractionation methods (such as ammonium sulfate precipitation) are used to separate most proteins from the cell extract, resulting in crude enzyme preparation. Gel filtration chroma......

• • A Gene Is Missing in the String: How to Proceed with Protein-Protein Interaction Analysis

  When a specific gene is absent from the analyzed DNA sequence, yet protein-protein interaction analysis remains necessary, the following strategies can be implemented: 1. Reassessing the DNA Sequence It is essential to verify the accuracy and completeness of the DNA sequence. In some cases, sequencing errors or omissions may prevent the identification of the target gene. Reanalyzing the sequence using various bioinformatics tools and databases can help detect missing or misannotated genes. 2. Identifying...

• • Why Is Protein Sequencing Mainly Based on Acid Hydrolysis and Supplemented by Alkaline Hydrolysis

  Protein sequencing predominantly relies on acid hydrolysis as the primary method, with alkaline hydrolysis serving as a supplementary approach for the following reasons: Higher Efficiency of Acid Hydrolysis Compared to alkaline hydrolysis, acid hydrolysis more efficiently cleaves peptide bonds, facilitating the breakdown of proteins into smaller peptides. This makes it the preferred method in protein sequencing. Under acidic conditions, peptide bonds are more susceptible to cleavage, generating peptide.....

• • Are the Data Obtained from LC-MS and Proton NMR the Same

  LC-MS (Liquid Chromatography-Mass Spectrometry) and ¹H NMR (Proton Nuclear Magnetic Resonance) are two distinct analytical techniques that yield fundamentally different types of data. LC-MS (Liquid Chromatography-Mass Spectrometry) 1. Function LC-MS is used to separate various components within a sample and determine their respective molecular weights. 2. Data It generates a mass spectrum that depicts the intensity of ions at different mass-to-charge ratios (m/z). 3. Advantages LC-MS enables the ........

• • What to Do If Excess Buffer Is Added During WB

  In Western Blot (WB) experiments, excessive buffer addition may adversely affect protein transfer efficiency, antibody binding, or signal detection. The appropriate corrective measures depend on the specific experimental stage at which the excess buffer was introduced. 1. Sample Preparation Stage If an excessive amount of lysis buffer or other sample preparation buffers is added: (1) Dilution: Additional sample material may be introduced to restore the intended buffer-to-protein ratio, provided this does...