What's the secret ingredient in beef jerky?
"Proteiny" usually indicates "umami", the so-called "fifth flavor" after sweet, sour, bitter, and salty.  It's triggered by glutamates.  Common sources of umami include beef, mushrooms, some seaweeds (most especially nori), rinds of some hard cheeses (most especially pecorino romano) and tomato paste.  I wouldn't be at all surprised if the store-bought jerkies you are comparing it to include monosodium glutamate, a common food additive that is essentially concentrated umami flavor.