Western blotting is a method for detecting a certain protein in a complex sample based on the specific binding of antigen and antibody. Different proteins can be divided into bands based on different mobility rates. The mobility is affected by many factors, which may cause the observed band size to be inconsistent with the expected size. The common factors include:

1. Post-translational modifications: For example, modifications such as glycosylation, phosphorylation, methylation, and acetylation will increase the molecular weight of the protein.

2. Splicing variants: Different expression patterns of various mRNA splicing bodies may produce proteins of different sizes.

3. Post-translational cleavage: Many proteins are first synthesized into precursor proteins and then cleaved to form active forms, such as COL1A1.

4. Relative charge: the composition of amino acids (the proportion of charged amino acids and uncharged amino acids).

5. Formation of multimers: For example, in protein dimer, strong interactions between proteins can cause the bands to be larger. However, the use of reducing conditions can usually avoid the formation of multimers.

If a protein in a sample has different modified forms at the same time, multiple bands may be detected on the membrane.