diff --git a/spectrum_io/search_result/maxquant.py b/spectrum_io/search_result/maxquant.py
index 161c9da..e68d830 100644
--- a/spectrum_io/search_result/maxquant.py
+++ b/spectrum_io/search_result/maxquant.py
@@ -62,6 +62,7 @@ def read_result(self, tmt_labeled: str) -> pd.DataFrame:
                 "MASS",  # = Calculated Precursor mass; TODO get column with experimental Precursor mass instead
                 "SCORE",
                 "REVERSE",
+                "PROTEINS",
             ],
             sep="\t",
         )
@@ -117,6 +118,7 @@ def update_columns_for_prosit(df: pd.DataFrame, tmt_labeled: str) -> pd.DataFram
             df["MODIFIED_SEQUENCE"] = maxquant_to_internal(df["MODIFIED_SEQUENCE"].to_numpy())
         df["SEQUENCE"] = internal_without_mods(df["MODIFIED_SEQUENCE"])
         df["PEPTIDE_LENGTH"] = df["SEQUENCE"].apply(lambda x: len(x))
+        df["PROTEINS"].fillna("UNKNOWN", inplace=True)
 
         return df