I can suggest a few additional ones that might be helpful depending on the specific cleavage pathways you're targeting. Here are some options to consider:

Protease Inhibitor Cocktail (Broad Spectrum): These cocktails typically contain a mix of inhibitors targeting serine, cysteine, and metalloproteases. A common commercial mix includes inhibitors for trypsin, chymotrypsin, and elastase, as well as leupeptin, pepstatin A, and others.

Serine Protease Inhibitors (e.g., PMSF or AEBSF): Phenylmethylsulfonyl fluoride (PMSF) and 4-(2-Aminoethyl)benzenesulfonyl fluoride (AEBSF) are good choices for targeting serine proteases. These can inhibit a range of proteases such as trypsin, chymotrypsin, and thrombin.

Metalloprotease Inhibitors (e.g., EDTA or 1,10-Phenanthroline): If you're dealing with metalloproteases, which are often implicated in protein cleavage, using EDTA or other chelators can help inhibit these enzymes by sequestering metal ions necessary for their activity.

Tissue Inhibitor of Metalloproteinases (TIMPs): These naturally occurring inhibitors target matrix metalloproteinases (MMPs). If your protein cleavage involves MMP activity, TIMPs can be used to block their function.

Neprilysin Inhibitors: If the cleavage you're observing involves neprilysin (an enzyme that degrades a wide variety of peptides), using neprilysin inhibitors (e.g., thiorphan) could help reduce cleavage.

Calmodulin-Dependent Protease Inhibitors (e.g., W-7): For calmodulin-dependent proteases, W-7 (a calmodulin antagonist) can be used to prevent the activation of calmodulin-dependent proteases.

If you're still seeing unwanted cleavage despite using these inhibitors, it may also help to adjust the lysis conditions, such as temperature or ionic strength, as well as the time of incubation. Sometimes, lower temperatures and rapid cell lysis can help minimize protease activity.

Is your tag at the C-terminus or N-terminus? If it's at the N-terminus, then it can be premature termination of translation for whatever reason.

Anyway, there are many various kinds of proteases and each of them requires specific inhibitor. Thus you need to use inhibitor coctail or try various inhibitors to see, which works for you.

It sounds like your protein is susceptible to cleavage by multiple proteases. Since you've already tested specific inhibitors (caspase, autophagy, calpain, and cathepsin inhibitors) without success, I would suggest using a broad-spectrum protease inhibitor cocktail. These cocktails typically contain inhibitors targeting serine, cysteine, aspartic, and metalloproteases, which should cover a wider range of proteases that might be responsible for the cleavage.

You can try commercially available protease inhibitor cocktails from Sigma-Aldrich, or Thermo Fisher, which are designed for cell lysates. If you suspect cleavage occurs before lysis, you might need to treat cells before harvesting, using cell-permeable inhibitors.

Dear, I recommend Protease Inhibitor Cocktail from TargetMol: https://www.targetmol.com/reagent/protease%20inhibitor%20cocktail

TargetMol Protease Inhibitor Cocktail C0001 consists of six components, including AEBSF, Aprotinin, Bestatin, E-64, Leupeptin, and Pepstatin A, which provide broad specificity against cysteine, serine, aspartic proteases, and aminopeptidases, without EDTA. This protease inhibitor cocktail has been optimized and tested using mammalian cell and tissue extracts. It effectively inhibits a wide range of proteases, including serine proteases and cysteine proteases, found in animal, plant, bacterial, yeast, and fungal samples. It is a convenient and reliable solution for protecting your proteins and is suitable for protein extraction from various tissue and cell types, allowing for more efficient isolation of target proteins.