Kafka Connect is a tool that allows you to stream data between Apache Kafka and other systems, sometimes the data might be converted from Protobuf to something different, other times, it might be converted to Protobuf.
Protobuf Converters
Confluent has a Protobuf Converter that can be used with any Kafka Connect Source or Sink, but it isn't as simple as it seems.
If you enable:
value.converter=io.confluent.connect.protobuf.ProtobufConverter
value.converter.schema.registry.url=http://localhost:8081